Use standard item spawning method in game::wish

Closes #1142. Also makes it so that jacqueshammer spawns with no gasoline, but that's due to the item definition file.
Set curammo properly in item constructor

Closes #1228. ACTUALLY closes #1142.
Unify and make sane the gun/tool unloading code

Closes #1242. Also makes it so that liquids don't get dumped on the ground if you're over-volume (since they can just go in another container).
Merge cleanup of unload code.