[MERGE] pull --overwrite for bundles

[Wouter van Heyst]

Wouter van Heyst has voted +1 (conditional).
Status is now: Conditionally approved
Comment:
The change looks good to me, but I'm not sure the test is complete?
In the added test tree_a.branch.revision_history() == 
tree_b.branch.revision_history()

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C45E5F60B.7030603%40utoronto.ca%3E