[lmi] Concinnity test for "xml files"

[Greg Chicares]

First of all, I seek a generic term for
  *.xml *.xrc *.xsd *.xsl
and have been calling them "xml files", for they all contain
  <?xml?>
; but is there a concise term that's more appropriate?

At any rate, please either make the files described above pass
'make check_concinnity', or let me know that it's not a good idea
to try. Things like the FSF address are easy and should be done.
But there's another test that passes files through 'xmllint' and
makes sure that filter doesn't change them; is that inappropriate
for '*.xs[dl]' files? We've found that test handy for catching
malformed xml before we commit it.

This isn't urgent: it would be good enough to address it within
the next couple of weeks.