Reviewed by john
        
        <rdar://problem/5099303> Deleting after a ToDo puts the caret in the wrong position

        Tests for the bug:
        * editing/deleting/5099303-expected.checksum: Added.
        * editing/deleting/5099303-expected.png: Added.
        * editing/deleting/5099303-expected.txt: Added.
        * editing/deleting/5099303.html: Added.
        Tests that extending an editable selection skips non-editable
        content:
        * editing/selection/5099303-expected.checksum: Added.
        * editing/selection/5099303-expected.png: Added.
        * editing/selection/5099303-expected.txt: Added.
        * editing/selection/5099303.html: Added.

WebCore:

        Reviewed by john

        <rdar://problem/5099303> Deleting after a ToDo puts the caret in the wrong position
        
        We were failing to create the correct selection 
        for DeleteSelectionCommand because the selection extension 
        operations don't skip over non-editable content for editable 
        selections.

        * editing/SelectionController.cpp:
        (WebCore::SelectionController::modifyExtendingRightForward):
        When extending an editable selection, don't extend into
        non-editable content.
        (WebCore::SelectionController::modifyExtendingLeftBackward):
        Ditto.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@20606 268f45cc-cd09-0410-ab3c-d52691b4dbfc