Heightfield_gt Update

I've updated (and replaced! That old file is out of there...) the plugin with the option of using up to 6 GL Clip Planes, to cull geometry.



Remember, this is based on the v002 Rutt Etra.plugin, and as such, all licensing is the same.

The clip planes are in eyespace coordinates (think pitch, yaw, roll sorta). No caveats apply to the application of clip planes (unlike the glClipPlane_gt.plugin).