BUG: OpenGLPolyDataMapper2D regression

OpenGLPolyDataMapper2D for OpenGL was clipping the z components between -1,0 or 0,1. The logic is a bit different in OpenGL2 versus OpenGL. I believe it has something to do with where the transformations are performed. I'm pretty sure z-clipping should not apply for 2D mappers. A new test was added that has polydata with a large z range.

NOTE: To see the bug, download this patch and revert to the original mapper:

git checkout master Rendering/OpenGL2

and ctest -R TestLegendBoxActor2