This patch implements the blur node for the realtime compositor. The patch is
still missing the Variable Size option because it depends on the Erode/Dilate
node, which is yet to be implemented. Furthermore, there are a number of
optimizations that can be implemented, the most important of which is the IIR
implementation of the Fast Gaussian filter, as well as the use of hardware
filtering and thread local memory. The latter of which was attempted but was
not robust enough, so it will be submitted as separate patch.
Differential Revision: https://developer.blender.org/D15663
Reviewed By: Clement Foucault
