[MERGE] ``bzr switch`` will attempt to find branches to switch to relative to the current branch

[John Arbash Meinel]

John Arbash Meinel has voted tweak.
Status is now: Conditionally approved
Comment:
I think we decided it should be re-raising the absolute URL exception, 
so that users get a cleaner error.

Otherwise I think we agreed on it.

For details, see: 
http://bundlebuggy.aaronbentley.com/request/%3C1204544440.10168.0.camel%40lifeless-64%3E