<rdar://problem/5078453> AXNext/PrevLineEndTextMarkerForTextMarker returns kAXErrorNoValue for attachment range
        
        Floating objects, such as aligned images, are not included as part of any line.  So when the given 
        text marker is on the floating object, the returned line edge cannot be found and asserts are fired.
        In addition, this paints an inconsistent text layout (in the accessibility sense) of where the floating 
        object resides.  Character/word methods report floating object at the beginning of the text line(s).  Yet
        line methods never present floating objects anywhere.  
        To fix this, the ax line methods will now do more checking to ensure floating object nodes are included
        when determining the line range/position. That way, assistive apps won't get stuck using the line methods 
        to read line-by-line

        * bridge/mac/WebCoreAXObject.mm:
        (updateAXLineStartForVisiblePosition):
        Added a helper method to adjust line start position to account for floating objects
        (-[WebCoreAXObject doAXLeftLineTextMarkerRangeForTextMarker:]):
        (-[WebCoreAXObject doAXRightLineTextMarkerRangeForTextMarker:]):
        (-[WebCoreAXObject doAXNextLineEndTextMarkerForTextMarker:]):
        (-[WebCoreAXObject doAXPreviousLineStartTextMarkerForTextMarker:]):
        Fixed up line routines to include floating object nodes in line position calculation.
        startOfLine/endOLine may return null for position next to a floating position.  So now there's extra checks to prevent
        returning null line position/ranges back to AX.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@21670 268f45cc-cd09-0410-ab3c-d52691b4dbfc