Reviewed by Anders.

    Reviewed by Anders.

        Fixed: <rdar://problem/5325262> REGRESSION (Tiger-Leopard): PictureTalk plug-in doesn't work

        The problem was that this particular plug-in handles "text/ptf", but WebCore wasn't giving the plug-in a chance to load
        any type with "text/"

        * dom/DOMImplementation.cpp:
        (WebCore::DOMImplementation::createDocument): Allow plug-ins to once again use "text/" MIME types, but only if the MIME
        type is not "text/plain". Disallowing plug-ins to use text/plain prevents plug-ins from hijacking a fundamental type
        that the browser is expected to handle, and also serves as an optimization to prevent loading the plug-in database in
        the common case.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@25166 268f45cc-cd09-0410-ab3c-d52691b4dbfc