Colour Management

- 1st stage: Linear Workflow

This implements automatic linear workflow in Blender's renderer. With the 
new Colour Management option on in the Render buttons, all inputs to the 
renderer and compositor are converted to linear colour space before 
rendering, and gamma corrected afterwards. In essence, this makes all 
manual gamma correction with nodes, etc unnecessary, since it's done 
automatically through the pipeline.

It's all explained much better in the notes/doc here, so please have a look:
http://wiki.blender.org/index.php/Dev:Source/Blender/Architecture/Colour_Management

And an example of the sort of difference it makes:
http://mke3.net/blender/devel/rendering/b25_colormanagement_test01.jpg

This also enables Colour Management in the default B.blend, and changes the 
default lamp falloff to inverse square, which is more correct, and much 
easier to use now it's all gamma corrected properly.

Next step is to look into profiles/soft proofing for the compositor.

Thanks to brecht for reviewing and fixing some oversights!

source/blender/editors/space_image/image_render.c

@@ -119,7 +119,7 @@ void imagewindow_progress(SpaceImage *sima, RenderResult *rr, volatile rcti *ren
 	if(rect32)
 		glaDrawPixelsSafe(x1, y1, xmax, ymax, rr->rectx, GL_RGBA, GL_UNSIGNED_BYTE, rect32);
 	else
-		glaDrawPixelsSafe_to32(x1, y1, xmax, ymax, rr->rectx, rectf);
+		glaDrawPixelsSafe_to32(x1, y1, xmax, ymax, rr->rectx, rectf, 0);
 	
 	glPixelZoom(1.0, 1.0);