The compostor used a fixed size of 4 floats to hold pixel data. this
patch will select size of a pixel based on its type.
It uses 1 float for Value, 3 float for vector and 4 floats for color
data types.
When benchmarking on shots (opening shot of caminandes) we get a
reduction of memory of 30% and a tiny speedup as less data
transformations needs to take place (but these are negligable.
More information of the patch can be found on
https://developer.blender.org/D627 and
http://wiki.blender.org/index.php/Dev:Ref/Proposals/Compositor2014_p1.1_TD
Developers: jbakker & mdewanchand
Thanks for Sergey for his indept review.
Seems to be simple non-initialized buffer used in math, but additional
check would be welcome here.
At least now result doesn't seems to be corrupted and seems to behaving
the same way as non-tile compositor.
