[whatwg] Document.setCapture/releaseCapture

Are setCapture/releaseCapture specified on document anywhere?  The last 
thing I see about it is 
http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2008-November/017415.html 
and then nothing...

Note that I suspect we do need a releaseCapture() so pages can call it 
without throwing, even if we decide it should do nothing when called.

-Boris