Filter out mtime difference of shared files on verify (rhbz#426672, #444661)

Filter out mtime difference of shared files on verify (rhbz#426672, #444661)
- Since we permit shared files to differ by mtime on installation, it makes
  no sense to consider them as verification failure either. This has been
  especially bad on multilib where timestamp differences make verify warning
  lights look like Las Vegas at night. If file mtime on disk and header
  differs, check if it's owned by more than one package and if so, ignore
  the timestamp difference.