Add header extension tag RPMTAG_FILESTATUS for file verification

Add header extension tag RPMTAG_FILESTATUS for file verification
- Permits basic file verification with just a headerGet(), with some
  caveats: there's no way to control which attributes get verified,
  and there's no filtering of mtime differences of shared files. Those
  aside, rpm -q --qf "[%{filestates:vflags} %{filenames}\n] <args>" now
  performs the same as "rpm -V --nodeps --noscripts <args>"