Reviewed by Eric.

        Some preparations for additive animations and animations in <use>.
        - Disallow animation elements in instance trees.
        - Fix buggy SVGUseElement::removeDisallowedElementsFromSubtree(), make it 
          public and static
        - Invoke it from SVGElementInstance::updateInstance() to clean up the instance tree
          there as well.
        - Add mechanism for blocking instance updates when an animation changes
          the referenced tree.
        
        The added assert in SVGSMILElement::insertedIntoDocument() verifies the fixes
        with the existing test cases.

        * svg/SVGAElement.cpp:
        (WebCore::SVGAElement::defaultEventHandler):
        * svg/SVGElementInstance.cpp:
        (WebCore::SVGElementInstance::updateInstance):
        * svg/SVGStyledElement.cpp:
        (WebCore::SVGStyledElement::updateElementInstance):
        (WebCore::SVGStyledElement::setInstanceUpdatesBlocked):
        * svg/SVGStyledElement.h:
        * svg/SVGUseElement.cpp:
        (WebCore::isDisallowedElement):
        (WebCore::SVGUseElement::removeDisallowedElementsFromSubtree):
        * svg/SVGUseElement.h:
        * svg/animation/SVGSMILElement.cpp:
        (WebCore::SVGSMILElement::insertedIntoDocument):
        (WebCore::SVGSMILElement::isSMILElement):
        (WebCore::SVGSMILElement::connectConditions):
        (WebCore::SVGSMILElement::disconnectConditions):
        * svg/animation/SVGSMILElement.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31891 268f45cc-cd09-0410-ab3c-d52691b4dbfc