UNIVERSAL EXPLOSIVE MATERIAL DETECTOR FIELD OF THE INVENTION The present invention relates to a universal detector for any explosive material, and methods therefor. BACKGROUND OF THE INVENTION In many environments, the atmosphere may contain vapors, gases, fluids or particles that are explosive. Explosives factories, armament depots, grain silos, flourmills, sawmills and many chemical factories and warehouses are just some of the many examples of places with potentially dangerous concentrations of explosive materials. The importance of early detection and prevention of catastrophic explosions in these places cannot be underestimated. Many devices have been developed over the years for the detection of explosive materials. Two broad classes of such detectors are known in the prior art. One class includes electrochemical detectors that check the concentration of known explosive fumes, vapors or gases in the atmosphere. A second class includes catalytic detectors that rely on changes in electrical resistance due to temperature rises. For example, British Patent GB876948 (1961) describes an explosive atmosphere detector in which an electrically heated catalytic wire causes combustion of the atmosphere. The wire is an electrical conductor disposed in a chamber maintained at an elevated temperature. The surface of the conductor is formed of a material, which at elevated temperatures sustains a catalytic combustion of the explosion-generative substances. The resulting temperature rise of the wire is detected by measuring the wire resistance. British Patent GB2314156 (1997) uses chemiluminescent emission to indicate the presence of explosive materials. One disadvantage of the prior art is that the device can only detect a known material. Quoting from Hazardous Gas Monitors, Jack Chou, McGraw-Hill Book Company, 200, chapter 3, page 45, "If two or more chemicals are involved, it is not even possible to calculate and determine the combustion range of the mixture." One cannot simply place a detector in an environment with unknown substances and expect the detector to provide advanced warning of dangerous concentrations of explosive materials. Anyone in charge of protecting and safeguarding a place with hazardous and potentially explosive materials must select detectors specifically made to detect those materials. Another disadvantage is that the detectors require periodic calibration. Yet another disadvantage, particularly of the second class of detectors, is that the detector does not provide a reliable indication if the actual concentration of the hazardous material found in the environment is at a dangerous level or not. Another drawback is that it is difficult if not impossible for detectors to detect and warn of the presence of an impending explosive situation in the case of explosive solid particles, such as a flourmill, sawmill, warehouse with cotton fibers in the air, etc. Another disadvantage of the prior art is that there is no known universal hazardous material detector. Every one of the known detectors is applicable only for a certain material or range or family of materials, but not any arbitrary material. SUMMARY OF THE INVENTION The present invention seeks to provide a novel universal detector (or monitor, the terms being used interchangeably throughout the specification and claims) for any hazardous explosive material, whether known or unknown, as is described more in detail hereinbelow. The detector may provide an early warning of an unsafe concentration of gases, fumes, vapors, liquids, and/or solid particles, and any combination thereof, which may be explosive. The prior art, as noted above, deals with measuring the concentration of the hazardous material(s) and then determining the explosiveness of the material(s) based on the measured concentration in accordance with accepted calculations and formulas. The methods of the prior art are dependent upon periodic calibration. The equipment used degrades with time. In contrast, in the present invention, there is no dependency on calibration or aging of the equipment. Throughout the specification and claims, the term "explosion" encompasses any kind of uncontrolled or controlled exothermic chemical or nuclear reaction, which may be accompanied by a sudden violent expansion of gas or fluids, heat, light, shock waves, or noise. "Explosion" is to be distinguished from "combustion" which merely involves burning of a substance in an oxygen-containing atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a simplified pictorial illustration of a hazardous material detector in an environment with a possibly explosive material, constructed and operative in accordance with an embodiment of the present invention; and Fig. 2 is a more detailed illustration of the hazardous material detector of Fig. 1. DETAILED DESCRIPTION OF EMBODIMENTS Reference is now made to Figs. 1 and 2, which illustrate a hazardous material detector 10, constructed and operative in accordance with an embodiment of the present invention. Detector 10 may be used to determine if a particular environment 12, such as but not limited to, an explosives factory, armament depot, grain silo, flourmill, sawmill, chemical factory and the like, has an unsafe concentration of gases, fumes, vapors, liquids, and/or solid particles, and any combination thereof, which may be explosive. In one embodiment, detector 10 may be locally mounted on a wall, ceiling, floor or other portion of a building or relevant structure in the environment 12. In another embodiment, detector 10 may be remotely located and connected to the environment 12, such as by suitable ducting 14 and possibly a fan 16. In yet another embodiment, detector 10 may be portable. Detector 10 may include a test chamber 18 having a receptacle 20 for holding a sample 22 from the environment 12. In contrast to the prior art, the sample 22 may contain any arbitrary substance that does not have to be known prior to testing. The test chamber 18 may be constructed of any suitable material and thickness able to withstand explosion of the sample 22, such as but not limited to, steel or reinforced concrete, with the possible addition of damping material (e.g., polyurethane or polystyrene), which may sacrificially cushion the effects of an explosion. The test chamber 18 may include an inlet 24 and fan 26 through which the sample 22 is drawn from the environment. Alternatively, as mentioned before, the fan may be external to the detector 10. It is noted that the detector 10 may monitor a single room or other area, or a multitude of rooms or areas. For example, many detectors 10 may be arranged in a network configuration to monitor samples 22 from many places, such as through ducting, air conditioning ducts and channels, chimneys, etc. A central console or command may oversee the operation and coordination of the detectors. Detector 10 may include excitation apparatus 28, adapted to explode, ignite, burn (or any combination thereof) the sample 22 or otherwise cause the sample 22 to explode. The excitation apparatus 28 may include, without limitation, one or more electrodes, detonators, spark plugs, firing caps, pyrotechnic devices and the like. The principle of detector 10 is elegantly simple: if the excitation apparatus 28 causes the sample 22 to explode, the environment 12 is considered hazardous, that is, explosive. The detector 10 does not "care" what the substance in the sample 22 is. The detector 10 does not "care" what the concentration of the substance in the sample 22 is. The detector 10 does not "care" if the substance is mixed or how it is mixed in the sample 22. Indeed the potentially dangerous situation in the environment 12 does not "care" about those things either. The detector 10 simply monitors, detects and provides advanced warning of the potentially dangerous, explosive situation in the environment 12. The explosion of the sample 22 may comprise a single explosion or a series of such explosions. The test chamber 18 may be sealed by any suitable seal 30, such as but not limited to, O-rings, gaskets and the like, made of synthetic or natural rubber or other elastomers, for example. Device 10 may further include one or more explosion sensors 31, such as but not limited to, a microphone, pressure sensor, temperature sensor or humidity sensor, for example, able to detect the onset of the explosion. The explosion sensor(s) 31 may be connected to a monitor or controller 33, which may provide a written, audible and/or visual indication and record of the explosion. Device 10 may further include a pressure device 32 operative to change the internal pressure in test chamber 18. The pressure device 32 may include, without limitation, any well-known pressure test chamber used in countless numbers of test laboratories, which does not need further description for the skilled artisan. In accordance with one non-limiting method of the invention, the sample 22 may be sealed in the test chamber 18 and pressure device 32 may be used to change the internal pressure therein, e.g., to elevate the internal pressure. By elevating the internal pressure, the conditions for explosion may be enhanced, that is, may be made artificially better for the hazardous event to occur than the actual conditions that currently prevail in the environment 12. This provides further advanced warning with a safety margin. Similarly, the conditions for explosion may be enhanced by adding a hazard- enhancement substance 34 into the test chamber 18 from a suitable source 36. For example, the hazard-enhancement substance 34 may include, without limitation, oxygen, fuel (e.g., gasoline, kerosene, or diesel), gunpowder, pyrotechnic substances, and others. The conditions for explosion may also be enhanced by elevating the temperature of the test chamber 18 with a heater 43. Once again, by artificially improving the conditions for the hazardous event to occur, further advanced warning may be provided with a safety margin. Other methods for artificially improving the conditions for the hazardous event to occur include, without limitation, changing the humidity in the test chamber 18 and/or changing the excitation energy level (e.g., voltage, current) of the excitation apparatus 28. It -will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of the features described hereinabove as well as modifications and variations thereof which would occur to a person of skill in the art upon reading the foregoing description and which are not in the prior art.