Fix sometimes leaving orphaned Portfiles in the registry
Fix sometimes leaving orphaned Portfiles in the registry

Portfiles are stored per subport,version,revision as there is no field
in the registry for the name shared between subports. Therefore, before
deleting a Portfile, we need to check only that the same subport is not
installed with different variants from an identical Portfile, not
whether *anything* else has an identical Portfile, since we can only
delete the one for this particular subport.

danchr/macports-base,macports/macports-base,danchr/macports-base,neverpanic/macports-base,macports/macports-base,neverpanic/macports-base