Blender Git Loki

Fix T40448: Blurring bug in the compositor

This commit pretty much reverts all the changes related on tile-ability
of the fast gaussian blur. It's not tilable by definition and would almost
always give you seams on the tile boundaries.

Atmind already met the issue and tried to solve it by increasing some
magic constant, which is pretty much likely simply made it so compositor
switched to full-frame calculation in that particular .blend file.

Fast gaussian is really not a production thing and need to be avoided.
We're to improve speed of normal gaussian blur instead.