Rev 1594: Fix common_ancestor to still calculate a common ancestor when ghosts are in /home/robertc/source/baz/integration/

[Robert Collins]

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revno: 1594
revision-id: robertc at robertcollins.net-20060322162609-fd4ba4a57afd33ed
parent: robertc at robertcollins.net-20060322132114-cc057ded01411a94
committer: Robert Collins <robertc at robertcollins.net>
branch nick: integration
timestamp: Thu 2006-03-23 03:26:09 +1100
message:
  Fix common_ancestor to still calculate a common ancestor when ghosts are
  present along all paths of ancestry - there are no 'import' revisions
  available.
modified:
  bzrlib/revision.py             revision.py-20050309040759-e77802c08f3999d5
  bzrlib/tests/test_graph.py     testgraph.py-20050905070950-42e6c958106610fd
  bzrlib/tests/test_revision.py  testrevision.py-20050804210559-46f5e1eb67b01289