Merged from trunk 7342:7351

   Merged from trunk 7342:7351

   +------------------------------------------------------------------------+
   | 7343    | Make --prune pull in the system set since that could pull in |
   | zmedico | some slots that wouldn't be pulled in otherwise.             |
   |---------+--------------------------------------------------------------|
   | 7344    | Prevent a potential KeyError when removing world from the    |
   | zmedico | digraph for --prune display.                                 |
   |---------+--------------------------------------------------------------|
   | 7345    | Document --depclean and --prune enhancements.                |
   | zmedico |                                                              |
   |---------+--------------------------------------------------------------|
   | 7349    | Make --update imply --oneshot since people often us it to    |
   | zmedico | update things when they don't want to add them to world.     |
   |         | Thanks to jakub for the suggestion.                          |
   |---------+--------------------------------------------------------------|
   | 7351    | Fix the reverse dependency display for --prune when there is |
   | zmedico | now real parent.                                             |
   +------------------------------------------------------------------------+

svn path=/main/branches/prefix/; revision=7353