Changes to image draw method options

It's now default to 2D textures, and no AUTO mode at this
moment, since detecting which method is the best not so
simple.

Image drawing could manually be switched to GLSL for tests
and feedback, but for default GLSL is not so much great.

Reason of this is huge images, where operations like panning
becomes dead slow comparing GLSL vs. 2D texture.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56385 954f8c5b-7b00-dc11-b283-0030488c597c
Cycles / SCons:
* Fast math compiler flag was set for Cycles, but not OSL. 

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@56386 954f8c5b-7b00-dc11-b283-0030488c597c