Just to clarify, all new documentation regarding MediaWiki should be added to mediawiki.org NOT meta.wikimedia.org.
There are still a lot of old pages on meta that are waiting to be transwikid, and these should still be edited on meta (rather than duplicating content) but any new pages should be created at mw.org.
Someone decided that most of mediawiki.org should be public domain instead of GFDL, thereby making any large scale movement of text from meta impossible.
So create gfdl.mediawiki.org, move or copy all the content from mediawiki.org to gfdl.mediawiki.org, and then merge in MediaWiki docs from meta.wikimedia.org.
But if we're going to talk about licenses, could we maybe please consider licensing gfdl.mediawiki.org (and/or MediaWiki docs on meta.wikimedia.org) under the GPL too, and allowing any documentation distributed with MediaWiki to be licensed under the GFDL (as well as the GPL). That way documentation could be freely copied backwards and forwards between the two (something that I suspect is sometimes happening already, but which is probably legally a bit dubious - but, of course, "I Am Not A Lawyer"). That way the code's documentation and all the documentation about the code would be under compatible licenses (which is not currently the case - ref: http://en.wikipedia.org/wiki/GFDL#GPL_incompatible_in_both_directions )
-- All the best, Nick.