[MERGE] Move write locking and write group responsibilities into the Sink objects themselves, allowing complete avoidance of unnecessary calls when the sink is a RemoteSink.

[Andrew Bennetts]

Andrew Bennetts has voted approve.
Status is now: Approved
Comment:
Seems ok.  Nice to see fetch.py shrinking a bit more, and I like the 
improved error handling the server-side smart method handler.

For details, see: 
http://bundlebuggy.aaronbentley.com/project/bzr/request/%3C1235510723.30336.6.camel%40lifeless-64%3E
Project: Bazaar