Merged from trunk 10816:10824

   Merged from trunk 10816:10824

   | 10817   | Generate and log eerror messages for any packages that need  |
   | zmedico | to be dropped due to unsatisfied dependencies when           |
   |         | --keep-going is enabled.                                     |

   | 10818   | Add documentation for the new --keep-going option.           |
   | zmedico |                                                              |

   | 10819   | Fix typo.                                                    |
   | zmedico |                                                              |

   | 10820   | Pass the digraph into the MergeTask constructor. It's        |
   | zmedico | currently unused but it will be useful for parallel          |
   |         | scheduling.                                                  |

   | 10821   | Break references from Package instances in the digraph       |
   | zmedico | before passing it into the MergeTask constructor.            |

   | 10822   | Remove the MergeTask._blocker_db attribute since it can just |
   | zmedico | be a local variable.                                         |

   | 10823   | Fix depgraph.break_refs() to work with DependencyArg         |
   | zmedico | instances (or anything else that may have a "root_config"    |
   |         | attribute).                                                  |

   | 10824   | Bug #226307 - Copy come code from                            |
   | zmedico | depgraph._iter_atoms_for_pkg() that was used to solve bug    |
   |         | #218854, and use it inside unmerge() when matching sets to   |
   |         | packages.                                                    |

svn path=/main/branches/prefix/; revision=10876