[MERGE] Add InterBranch.push().

[Ian Clatworthy]

Ian Clatworthy has voted tweak.
Status is now: Conditionally approved
Comment:
There are numerous effort tests now in branch_implementations/test_push. 
Should these be copied across now? If so, doing so in a follow-up patch 
is OK by me.

Given our lack of copy tracking :-( , I think it's worth putting a 
comment in your test_push.py file as to where most the content came 
from. Also, this import in __init__.py can be combined with the line 
above ...

+from bzrlib.tests import TestCaseWithTransport


For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C20090330195548.4D7AB1D358%40ganieda.vernstok.nl%3E
Project: Bazaar