Merged from trunk 11139:11147

   Merged from trunk 11139:11147

   | 11140   | Use the memoized _choose_pkg() result to return earlier from |
   | zmedico | _schedule_tasks() when possible.                             |

   | 11141   | Calling _schedule() from Scheduler._poll() is unsafe since   |
   | zmedico | the _schedule() call itself can consume poll events.         |
   |         | Therefore, until a safe way exists, don't do it.             |

   | 11142   | Fix Scheduler._schedule_tasks_imp() so that it never         |
   | zmedico | indicates that there are remaining tasks in cases when it's  |
   |         | supposed to bail out due to a package failure.               |

   | 11143   | Merge tasks currently run synchronously which makes it       |
   | zmedico | necessary to disable auto_schedule on the merge queue in     |
   |         | order to avoid excess recursion which prevents tasks from    |
   |         | being marked complete as soon as they should be.             |

   | 11144   | Make PollScheduler._poll() add poll events to the stack      |
   | zmedico | instead of returning them. This makes it more useful as a    |
   |         | hook, allowing Scheduler._poll() to safely call _schedule(). |

   | 11145   | * Clean up _schedule_tasks_imp() a bit. * Make _task()       |
   | zmedico | access _background directly instead of as a parameter.       |

   | 11146   | Fix Scheduler emergelog() interaction to properly disable    |
   | zmedico | emergelog() xterm titles whenever the status display is      |
   |         | enabled.                                                     |

   | 11147   | Redirect some more unmerge() output through writemsg_level() |
   | zmedico | so that it can filtered out when in background mode.         |

svn path=/main/branches/prefix/; revision=11149