Merged from trunk 7130:7135

   Merged from trunk 7130:7135

   +------------------------------------------------------------------------+
   | 7131    | Clean up system and world set handling. For forward          |
   | zmedico | compatibility, the world file handling now allows the world  |
   |         | file to contain arbitrary atoms such as slot atoms.          |
   |---------+--------------------------------------------------------------|
   | 7132    | Add USE to the list of metadata keys to pull.                |
   | zmedico |                                                              |
   |---------+--------------------------------------------------------------|
   | 7133    | Fix broken favorites handling with --usepkg.                 |
   | zmedico |                                                              |
   |---------+--------------------------------------------------------------|
   | 7135    | Implement BlockerCache.keys() so that DictMixin.__repr__()   |
   | zmedico | works.                                                       |
   +------------------------------------------------------------------------+

svn path=/main/branches/prefix/; revision=7137