Merged from trunk 10988:10996

   Merged from trunk 10988:10996

   | 10989   | * Call self._wait() when unregistering output handlers, in   |
   | zmedico | order to avoid triggering a tight loop. Also fix             |
   |         | Subprocess._wait() to only schedule when self.registered is  |
   |         | True. * Add an assertion inside Scheduler._schedule_main()   |
   |         | to try and detect tight loops like the one above. * Fix typo |
   |         | in Scheduler._merge_exit().                                  |

   | 10990   | Remove redundant call to _schedule_main().                   |
   | zmedico |                                                              |

   | 10991   | Fix Scheduler._dependent_on_scheduled_merges() to properly   |
   | zmedico | distinguish "nomerge" nodes from "uninstall" nodes.          |

   | 10992   | In scheduler._schedule_main(), only consider a poll() event  |
   | zmedico | to be a state change if it results in a handler being        |
   |         | unregistered.                                                |

   | 10993   | Make the "tight loop" assertion trigger whenever there is no |
   | zmedico | state change detected for a given _schedule_main() call.     |

   | 10994   | * Fix _choose_pkg() to pop the first node if there are no    |
   | zmedico | other jobs running. * Allow _choose_pkg() to choose an       |
   |         | uninstall node when it reaches the front of the queue. TODO: |
   |         | fix order for uninstall operations. * Fix                    |
   |         | _dependent_on_scheduled_merges() to handle direct circular   |
   |         | deps correctly.                                              |

   | 10995   | Fix _prune_digraph() to correctly distinguish "nomerge"      |
   | zmedico | nodes from "uninstall" nodes.                                |

   | 10996   | Fix Scheduler._choose_pkg() to perform uninstallation        |
   | zmedico | actions (due to blockers) in the correct order when building |
   |         | in parallel.                                                 |

svn path=/main/branches/prefix/; revision=11000