Some color space issues in sequencer:

Sequencer was always trying to do GLSL color space
conversion, not respecting user settings at all.

This failed a lot when RGB curves a used in color
management settings.

Now sequencer will fallback if GLSL can not be used
and will also respect user settings (however, draw
pixels are not supported, sequencer always uses 2D
textures).

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56340 954f8c5b-7b00-dc11-b283-0030488c597c