Reviewed by John

    Reviewed by John

        Fix for this bug:

        <rdar://problem/3900996> Crash dragging past end of contentEditable DIV, at DOM::RangeImpl::pastEndNode() const + 24

        * khtml/xml/dom_position.cpp:
        (DOM::Position::equivalentRangeCompliantPosition): Fixed this function so that it constrains the offset
        of the position to be >= 0 and <= number of kids of its node. Not doing this constraining led to a DOM
        exception trying to use a Position returned from this function to set the boundary point of a Range (which
        eventually led to the crash). Since this crash happened, it seems like this function was failing in its
        contract to return a range-compliant position, hence the need for this fix.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@8100 268f45cc-cd09-0410-ab3c-d52691b4dbfc