Improve performance of border drawing by minimizing calls to...

Improve performance of border drawing by minimizing calls to Surface::getTopologyHelper().  When drawing borders, the border point coordinates are converted from barycentric to cartesian coordinates and Surface::getTopologyHelper() was called for each point in the border.  This has been changed so that Surface::getTopologyHelper() is called once for each border and the topology helper is then passed as a parameter to the conversion process for each point.  On my Mac, this resulted in about a 20% reduction in time required to draw a large number of surfaces with many borders.  Apple's Instruments Tool had indicated that significant time was spent in locking and unlocking of the mutex in Surface::getTopologyHelper.
Also, fixed drawing of 'Lines' border drawing so that it uses OpenGL line segments so that when 'unstretched lines' is enabled, segments can be skipped.