Blender Git Loki

Object Mode: Grid: Add a non-hard depth test.

This adds a custom depth test that have the benefits to glitch less and be more visually pleasing.
Downside is that it let the grid pass trough the objects a little.

This effect is done in NDC space so that it counteract the logarithmic depth distribution imprecision (read as it's less visible near the camera but more present far away).

This patch also includes some cleanups.