Merged from trunk 9941:9959

   Merged from trunk 9941:9959

   | 9943    | Make dir_get_metadata() retry if a httplib.ResponseNotReady  |
   | zmedico | exception occurs.                                            |

   | 9945    | Bug #172812 - Add an Uninstall class derived from the        |
   | zmedico | Package class, for packages that may need to be uninstalled  |
   |         | to avoid conflicts.                                          |

   | 9946    | Bug #172812 - Automatically uninstall packages to avoid      |
   | zmedico | blocker conflicts. The intention is to only uninstall        |
   |         | packages that would be removed by --depclean (after the      |
   |         | updates) anyway. To prevent automatic uninstallation of      |
   |         | packages that the user probably wants to keep, the following |
   |         | types of packages will not be automatically unmerged: *      |
   |         | Installed packages that have been pulled into the current    |
   |         | dependency graph. Note that this check is not necessarily    |
   |         | complete unless the --complete-graph option is enabled,      |
   |         | making other sanity checks necessary. * Installed packages   |
   |         | matched by atoms from the system set. For safety, these are  |
   |         | unmerged after being replaced by another version. *          |
   |         | Installed packages matched by atoms from the world set, if   |
   |         | there is no matching replacement in the current dependency   |
   |         | graph.                                                       |

   | 9947    | s/unmerge/uninstall/ for consistency.                        |
   | zmedico |                                                              |

   | 9948    | Bug #172812 - Document new automatic uninstallation behavior |
   | zmedico | in the "Conflict Avoidance" section.                         |

   | 9949    | Bug #172812 - Protect packages from being removed from the   |
   | zmedico | world file during automatic uninstallation.                  |

   | 9950    | Reset the state variables for leaf node selection in         |
   | zmedico | depgraph.altlist() when appropriate.                         |

   | 9951    | Split out a _dequeue_uninstall_tasks() method.               |
   | zmedico |                                                              |

   | 9952    | Bug #172812 - When automatically uninstalling packages,      |
   | zmedico | build the next package in the merge list before executing    |
   |         | scheduled uninstall tasks.                                   |

   | 9953    | Combine --nodeps spinner logic.                              |
   | zmedico |                                                              |

   | 9954    | Fix broken mtimedb resume list handling for automatic        |
   | zmedico | uninstall tasks.                                             |

   | 9955    | Handle potential InvalidDependString exceptions when match   |
   | zmedico | packages to system and world atoms in depgraph.altlist().    |

   | 9956    | Fix interaction between automatic uninstall and options like |
   | zmedico | --pretend, --fetchonly, and --buildpkgonly.                  |

   | 9959    | Add a note about automatic uninstallation to solve blockers. |
   | zmedico |                                                              |

svn path=/main/branches/prefix/; revision=9962