Merged from trunk 11616:11618

   Merged from trunk 11616:11618

   | 11617   | Make depgraph._add_pkg() take a Dependency instance. This    |
   | zmedico | provides access to the atom which pulled in the package,     |
   |         | which may be needed in order to verify that a different      |
   |         | package that's been added to the graph is capable of         |
   |         | satisfying the atom.                                         |

   | 11618   | Fix depgraph._add_pkg() to ensure that the existing package  |
   | zmedico | in the graph matches the required atom in cases when a       |
   |         | different package has been passed in. This solves a problem  |
   |         | with silently unsatisfied USE deps that was reported by      |
   |         | Jorge Manuel B. S. Vicetto <jmbsvicetto@g.o>. Now the        |
   |         | unsatisfied dependency will result in a "slot conflict"      |
   |         | rather than be silently ignored.                             |

svn path=/main/branches/prefix/; revision=11620