Move two old functions to compat.lua

This commit also removes doPlayerChangeName, because updating a
creatures name after it has been placed is too complex in the protocol
(the function didn't do that anyway, and updating name in the database
can be done with a SQL query if necessary).
Move /addskill to talkactions

This commit implements feature request #255
Fix bug in doPlayerAddExp
Fixes #261
Merge pull request #263 from ninjahopparn/master

Fixes #261