[merge] restore 'bzr push' within a single repository

[Robert Collins]

Robert Collins has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
Looks good, though I dont think the right place to test pushing between 
two branches in the same repository is our UI tests. Instead, it should 
be in branch_implementations, so that different format branches get the 
test exercised. Not all branches work with shared repositories - but 
doing self.make_repository('.', shared=True) in the test, should do the 
right thing for the test suite IIRC.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C45D0ED91.8050509%40arbash-meinel.com%3E