<rdar://problem/4204892> Correcting incorrect spelling in Mail causes others to lose their red squiggles

        Fixed by having SplitTextNodeCommand::doApply copy the markers to the new node, and having SplitTextNodeCommand::doUnapply
        copy the markers from the merged-in node to the combined node.

        btw - filed <rdar://problem/4256492> "WebCore editing automated layout tests verify spelling markers"
        so that we can automate tests for this.

        Test cases added:
        * manual-tests/keep_spelling_markers.html: Added.

        * khtml/editing/split_text_node_command.cpp:
        (khtml::SplitTextNodeCommand::doApply):
        (khtml::SplitTextNodeCommand::doUnapply):
        Call new copyMarkers() function.

        * khtml/xml/dom_docimpl.cpp:
        (DocumentImpl::removeMarkers):
        (DocumentImpl::addMarker):
        (DocumentImpl::copyMarkers):
        (DocumentImpl::markersForNode):
        (DocumentImpl::shiftMarkers):
        * khtml/xml/dom_docimpl.h:
        (DOM::DocumentMarker::):
        Added copyMarkers() function.  Reorganized code for clarity.

        * khtml/xml/dom_textimpl.cpp:
        (CharacterDataImpl::setData):
        (CharacterDataImpl::deleteData):
        (CharacterDataImpl::replaceData):
        * kwq/KWQKHTMLPart.mm:
        (KWQKHTMLPart::respondToChangedSelection):
        * kwq/WebCoreBridge.mm:
        (-[WebCoreBridge unmarkAllMisspellings]):
        Update calls to marker functions.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@10530 268f45cc-cd09-0410-ab3c-d52691b4dbfc