Flamethrower fixes.

Fuel now burns, even without an auto-ignition temperature, which was a silly way of doing things.
Mobs no longer ashify since their proc is changed.
Flamethrowers now spread more fuel and burn more consistently for it.
Atoms now have volatility, so they can burn more if they have less fuel.
EOL.
Merge pull request #2147 from ComicIronic/FlameThrows

Flamethrower fixes.