Make LyXML->xml2rfc XSL not error out

Nor warn.

It doesn't work right now, but it doesn't error out.
Make lyx2xml work, though hackishly

For now I'm including a copy of parser_tools.py from LyX, but this is
undesirable as that's GPLed.  Need to re-write the needed functions and
include them in lyx2xml.py itself.