Code review comment for lp:~nmb/bzr/script-test-mv

Using os.rename() instead of shutil.move() will make the limitations more obvious.

The long term plan is to move to a transport-based implementation where moving
across file systems will not be supported anyway.

A final test to check the behaviour when the file does not exist... reveals untested code
(error was called with a single path) :)

I'll tweak and merge.