Item drops

[xoft]

Okay, I refactored the item dropping code. Right now it drops single pickups even for multiple same items. But should we want to change this behavior, it wouldn't be too difficult to do, it's all centralized in two functions, cWorld::SpawnItemPickups().
I'm not playing with that anymore, because that part of the code is really really boring to write (check out the cBlockToPickup::ToPickup() function, that was a nightmare! )