[MERGE] Set allow_optimize=False when spilling btree content to disk

[Robert Collins]

Robert Collins has voted approve.
Status is now: Approved
Comment:
Given you added the allow_optimise stuff in the first place... I'm not 
entirely sure that tapping out on it being inaccessible for tests makes 
that much sense. Certainly agree that its the right thing to do and the 
code looks ok.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C49C2A9C1.6090500%40arbash-meinel.com%3E
Project: Bazaar