Code review comment for lp:~jspashett/bzr/322807_add_root_drive_windows

In _cicp_canonical_relpath (osutils.py)

This is done:
return current[len(abs_base)+1:]

Which does not work on windows, where abs_base = x:/ in this case a '/' is not appended since it already ends with one, making len(abs_base)+1 incorrect in this case.

Change to use os.path.split instead.