Merged from trunk 8032:8036

   Merged from trunk 8032:8036

   | 8033    | Unify the masking reasons output so that the same code path  |
   | zmedico | is used for both ebuilds and binary packages.                |

   | 8034    | Initialize the list of package repos inside the depgraph     |
   | zmedico | constructor so it's always available.                        |

   | 8035    | Migrate depgraph.select_files() to use the filtered repo for |
   | zmedico | expansion of greedy atoms. Also, use the list of repos to    |
   |         | clean up the category expansion code.                        |

   | 8036    | Cache IUSE in bindbapi to optimize --newuse calculations.    |
   | zmedico | Also, fix filtering code for reading/writing USE and IUSE    |
   |         | from/to the metadata index.                                  |

svn path=/main/branches/prefix/; revision=8074