[MERGE] Add InterBranch.

[John Arbash Meinel]

John Arbash Meinel has voted resubmit.
Status is now: Resubmit
Comment:
The implementation seems okay, as it is just another InterObject code.

However, this has no tests.

Since it is going to be a point of implementations, we should probably 
add a "bzrlib.tests.per_interbranch" directory with a 
"test_update_revisions". You can probably crib most of that from one of 
the "bzrlib.tests.interX" test suites.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090211150929.D9B03574FA%40charis.vernstok.nl.vernstok.nl%3E
Project: Bazaar