Merges the two meteor events into one, and now takes severity into consideration instead.
Including the basic meteors there are also new types ranging from flaming to radioactive which may drop appropriate types of ore.
Committing this early to allow pete to commit something involving the .dme file which would probably conflict otherwise.
git-svn-id: http://tgstation13.googlecode.com/svn/trunk@4514 316c924e-a436-60f5-8080-3fe189b3f50e