Reviewed by Geoff.

        Testcases for http://bugs.webkit.org/show_bug.cgi?id=11777
        Crash when using XMLSerializer.serializeToString() on
        documentless, DocumentType nodes.

        * fast/dom/XMLSerializer-doctype-expected.txt: Added.
        * fast/dom/XMLSerializer-doctype.html: Added.
        * fast/dom/XMLSerializer-doctype2-expected.txt: Added.
        * fast/dom/XMLSerializer-doctype2.html: Added.

WebCore:

        Reviewed by Geoff.

        Fix for http://bugs.webkit.org/show_bug.cgi?id=11777
        Crash when using XMLSerializer.serializeToString() on
        documentless, DocumentType nodes.

        Test: fast/dom/XMLSerializer-doctype.html
        Test: fast/dom/XMLSerializer-doctype2.html

        * dom/DOMImplementation.cpp:
        (WebCore::DOMImplementation::createDocument): set the document of the 
        DocumentType node to the new document.
        * xml/XMLSerializer.cpp: Cleanup.
        (WebCore::XMLSerializer::serializeToString): now throws an exception
        for documentless nodes. 
        * xml/XMLSerializer.h: cleanup
        * xml/XMLSerializer.idl: add exception



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@18085 268f45cc-cd09-0410-ab3c-d52691b4dbfc