work-around the same location being reinstalled thru a different path

work-around the same location being reinstalled thru a different path
later... no need to do anything on sets consisting purely of "kept" handles

This is not fully satisfying, I expect I need to tie some "done already" to
locations as we do with sets, so that we can wipe update_info properly and
be done once and for all...

Issue found by stsp@ while trying to use FETCH_PACKAGES, which is still not
100% in good shape with this.