BRANCH 4.2:
  renamed free_copy as copy, free_move as move, and the default is "create" mode for file/directory/group checkin
  In ThumbCmd check for if extension is in normal file extension list. It was checking the path instead which is incorrect.
  made Config.get_value() tolerate a simple string config when sub_key is used.
  added support for copy directory in FileUndo.create()