Allows for easier customizing of whether or not an item should be shared with players upon pickup in co-op (e.g. it allows it to be expanded to weapons with custom cvars).
Localized functionality to an inventory function so that any item can make use of sharing. Added flag to avoid infinite recursions. HandlePickup() will now also share keys (for more complete handling). PuzzleItems are now included in sharing.
* Key.ValidLock: returns whether a lock number is valid (can be unlocked) or belongs to a "does not work" door.
* Key.GetMapColorForLock: returns the automap color for a lock number (or -1 if the lock isn't valid).
* Key.GetMapColorForKey: likewise, but for a specific key.
