[Mesa-dev] SSO fixes V3

[Timothy Arceri]

V3:
- Fixed explicit location optimisation (Patch 1)
- Added fix for assigning varyings to the same location when
 using arrays (Patch 6)
- Pushed some clean-up patches reviewed in v2

V2: I've dropped most of my fix from V1 and instead included the fixes
from Gregory which I have cleaned up slightly. I've also added a
patch to remove inactive varyings with an explicit location.

The removal of inactive varyings with an explicit location results
in no changes in the public shader-db although its unlikely many if any
shaders in there make use of SSO.

I also ran the series on Intels CI system with no regressions.

The series fixes the following piglit tests:

piglit.spec.arb_separate_shader_objects.rendezvous by name
piglit.spec.arb_separate_shader_objects.rendezvous by name with multiple interpolation qualifier
http://patchwork.freedesktop.org/patch/66094/