[MERGE] Remove Branch.get_transaction

[Robert Collins]

Robert Collins has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
NEWS should mention your name. The _clear_revision_history_cache method 
could actually be less specific usefully: it seems to me that any other 
cached data should be cleared on unlock etc, so having overly precise 
methods isn't that useful. (Of course the method to cache it should be 
specific :). Perhaps you could have a '_clear_branch_cache()' which 
calls '_clear_revision_history_cache()' for now, if you feel that 
overriding the caching mechanism is important.

Please read the docstrings on your new methods. They dont all parse.

Lastly, the IdentityMap logic related to revision_history should be 
nuked; its now cruft.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070326051958.GB7005%40steerpike.home.puzzling.org%3E