Registration of media type model/x3d+XXX

[MURATA Makoto]

The +xml suffix is specified in RFC 4288 and RFC 3023, while the vrml
suffix and +binary suffix are not.  Thus, x3d+vrml and 
x3d+binary should be renamed.

Cheers,

-- 
MURATA Makoto <murata at hokkaido.email.ne.jp>