[MERGE] Add a smart method method that can pull a set of revisions in a single request

[Aaron Bentley]

Aaron Bentley has voted resubmit.
Status is now: Resubmit
Comment:
This looks pretty good.  I still don't see a direct test for 
self.item_keys_introduced_by, though.  Without that, there's no 
justification for implementing it on RemoteRepository.

cdiff --check-style complains that there are 7 lines with trailing 
whitespace, and 10 that exceed 79 columns.  Please clean up.

I know we plan to get the smart server running on bazaar-vcs.org, but we 
shouldn't put this version on until that repository has been reconciled.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C20070831054633.GL12130%40steerpike.home.puzzling.org%3E