Merged from trunk 9869:9891

   Merged from trunk 9869:9891

   | 9870    | Make _dep_check_composite_db match() return multiple slots   |
   | zmedico | so that it behaves more like other dbapi instances would,    |
   |         | and also make it inherit from dbapi.                         |

   | 9871    | Fix _dep_check_composite_db.match() so that it doesn't       |
   | zmedico | exempt the highest slot from visibility checks.              |

   | 9872    | Fix the _dep_check_composite_db visibility filtering some    |
   | zmedico | more.                                                        |

   | 9873    | Improve lookahead for new-style virtuals: * Substitue the    |
   | zmedico | graph tree for the vartree in dep_check() since we want atom |
   |         | selections to be consistent with package selections have     |
   |         | already been made. * Add the selected package to the graph   |
   |         | as soon as possible so that later dep_check() calls can use  |
   |         | it as feedback for making more consistent atom selections. * |
   |         | Expand all slots of new-style virtuals inside                |
   |         | _dep_check_composite_db so that lookahead examines a matched |
   |         | slots. This solves some cases of bug #1343, and extends the  |
   |         | fix for bug #141118 to work in cases when a virtual is not   |
   |         | yet installed but it has been pulled into the graph.         |

   | 9874    | To optimize consistency of atom selections, add all of the   |
   | zmedico | root packages to the graph before processing any             |
   |         | dependencies.                                                |

   | 9879    | * For optimal atom selection, use PackageVirtualDbapi        |
   | zmedico | instances in place of the vardb for all dep_check() calls. * |
   |         | Replace dep_check_trees in depgraph.validate_blockers() with |
   |         | the equivalent self._graph_trees reference.                  |

   | 9881    | Fix buggy logic in WorldSet.load() that causes it to discard |
   | zmedico | all of it's atoms in some cases (leading to loss of the      |
   |         | whole world file).                                           |

   | 9882    | Fix some more broken logic inside WorldSet.load().           |
   | zmedico |                                                              |

   | 9883    | s/timetasmp/timestamp/                                       |
   | zmedico |                                                              |

   | 9884    | Split out a depgraph._add_dep() method.                      |
   | zmedico |                                                              |

   | 9885    | Call depgraph._add_dep() to add package dependencies to the  |
   | zmedico | graph as soon as possible rather than pushing them onto the  |
   |         | stack.                                                       |

   | 9886    | Fix some breakage in the allow_unsatisfied handling.         |
   | zmedico |                                                              |

   | 9890    | When regenerating USE_EXPAND in config.setcpv(), improve     |
   | zmedico | performance by using regular expression instead of           |
   |         | str.startswith().                                            |

   | 9891    | Revert back to using startwith because I screwed up my       |
   | zmedico | benchmark and it turns out starswith is faster than using    |
   |         | regular expressions.                                         |

svn path=/main/branches/prefix/; revision=9893