bzr merge NON-EXISTENT-RELPATH

[Denys Duchier]

One of my students made a typo and we discovered that:

    bzr merge A/B/C

where A/B/C does not exists, simply prints "nothing to do" instead of
complaining that A/B/C does not exist.

This is because of the Branch.open_containing in _get_merger_from_branch
opening the current branch (defaulting to local transport).

Why are we using open_containing here?  does it make sense?

Cheers,

--Denys