[merge] cleanups in upgrade

[Martin Pool]

Tim and I did some work towards doing upgrade on the server side.
Here is a preliminary patch:

 * move some code to make backups from upgrade.py in to bzrdir, where
it can be either customized per implementation or run more cleanly on
the server

 * needs_format_conversion(format=None) used to imply upgrading to the
default format; now it's deprecated.  This is only called from inside
upgrade (or maybe plugins) so I think the need for convenience is
questionable, and being explicit is better.

-- 
Martin <http://launchpad.net/~mbp/>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: 20090116-upgrade.diff
Type: text/x-diff
Size: 17093 bytes
Desc: not available
Url : https://lists.ubuntu.com/archives/bazaar/attachments/20090116/8e127c8a/attachment-0001.bin