Cut Selection can select Through Mesh

[jlopezbi]

when selecting meshEdges as cuts one can accidently select an edge on the opposite side of the mesh, even though it is not visible. Solutions:

• check if selected mesh edge is visible, only do stuff if it is
• somehow apply filter for only visisble edges
• somehow find set of visible edges leads: http://discourse.mcneel.com/t/mesh-faces-inside-frustum-visibility-of-mesh-faces/9294/6 Clip Coordinates https://en.wikipedia.org/wiki/Clip_coordinates