Blender Git Loki

Two fixes in one commit.

- The ortho render recode had a weak method to calculate the Z value of the
render coordinate (shi.co[2]). Worked OK for normal render, but not in
unified, giving big errors in Ortho Unfied render.
Solved with proper math, using face equation a*x+b*y+c*y=d. Dunno why I
didn't do it in first place. :)

- Bug fix #2493. Edge render gave much different result for Ortho. This
was due to overflows in the integer math filtering zbuffer values.
Cleaned it op properly, preventing any integer overflow now.