* Napalm works again, which fixes incendiary grenades.
 * Stopped the fuel and n20 option, in spawn_air, from runtiming.
 * Added toxins as a spawn_air option.
 * Removed all use of the fuel option and replaced it with toxins, since fuel does not work with LINDA anymore.
 * Made atmos_spawn_air() use flags.
 * Replaced "fire" with SPAWN_HEAT. You will have to use it in conjunction with SPAWN_TOXINS to spawn fire.
 * Added flags for HEAT, COLD, TOXINS, OXYGEN, CO2, NITROGEN, N2O, FUEL and AIR.
 * Made frostoil use SPAWN_COLD when used on a turf.
 * Removed the spawn fuel option.
 * Removed SPAWN_COLD
Merge pull request #1507 from Giacomand/napalm

Napalm works again, which fixes incendiary grenades.