svg, mathml, multipart, xml (because of namespace) are forbidden.
the charset parameters in Content-Type is only set when it is by the original server.
the */xhtml+* Content-Type : the conversion to UTF-8 is now done (it wasn't the case before).
string type is used because of the mime package API.
git-svn-id: file:///srv/svn/repo/yukari/trunk@63 f3bd38d9-da89-464d-a02a-eb04e43141b5