Add support to depgraph._select_atoms() to take a "parent" parameter

Add support to depgraph._select_atoms() to take a "parent" parameter
and use that to try and avoid unresolvable direct circular dependencies
when necessary. Also, make atom selection more consistent with the
graph to solve some cases of bug #1343. This improves the fix from
bug #141118 to work in cases when a virtual is not yet installed but
it has been pulled into the graph. For example, see the case of
Bug #163801#c17, where we want kaffe to satisfy virtual/jdk-1.4
without an extra jvm being pulled in unnecessarily. (trunk r9901)

svn path=/main/branches/2.1.2/; revision=9903