-Add support for the ZDoom DeHackEd weapon extensions "Ammo use" and "Min ammo" and "Ammo per shot" from Eternity.
-Set "Ammo use" and "Min ammo" for the BFG if DeHackEd changes "BFG Cells/Shot".
-Remove the fixed ammo usage of 10 for railguns and instead decrease by "Ammo use" and change weapons if the railgun does not have "Min ammo" (bug 971). Note that if the DeHackEd patch that implements the railgun does not otherwise specify, the railgun will use the amount of ammo per shot as the weapon it replaces.

git-svn-id: http://odamex.net/svn/root/trunk@3832 b0bcef46-2027-0410-bd56-ab726e9a1d04