Added itemID() function to robots, allowing them to extract the ID,
subtype, and name of an item inside the inventory.

Extended compare() and compareTo() to also return the difference of the id
+ (subtype/1000) of both items being compared. This allows for item
sorting. The first returned value is still a boolean, so this should be
backwards compatible with existing Lua scripts.

Didn't overwrite a bunch of changes in the upstream this time, either!