repo group: fix logging of rename/move

After renaming a group, it would iterate over all the contained groups and
repos and update their full path while logging the update from the/old/path to
the the/new/path. Doing that, it would also visit the already renamed top level
group, but since the full path of that one already had been updated, it would
log it as renaming from the/new/path to the/new/path.

Fixed by logging when renaming in the first place, and skipping the top level
repo group while iterating.

To avoid redundant logging, only log (and rename) if the name or parent
actually change.

Based on a patch by toras9000.