Tweak openoffice-4 to use private copy of saxon and bump portrevision.
See https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=193776.
This requires a new version of the ext_sources tarball.
Modernize MASTER_SITES syntax and update MASTER_SITE for unowinreg.dll.
Update comment to take de facto mainternship.