Make the entire code portable to other, custom mods
Correct register_on_dieplayer to register_on_leaveplayer
Do not close shop formspec when setting the title using enter
This limits the tools a shop will accept or give to those whose wear is less
than or equal to the tool shown in the Owner needs or Owner gives lists. This
protects both owners and customers from unfair trades. Owners are protected
from receiving worn out tools when a new tool is placed in the needs list.
Customers are protected from receiving worn out tools when a new one is placed
in the give list.
