[MERGE] Cache ghosts when we can get them from a RemoteRepository in get_parent_map.

[Bundle Buggy]

Bundle Buggy has detected this merge request.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C1237878903.15722.652.camel%40lifeless-64%3E
Project: Bazaar