[Piglit] GL_ARB_explicit_attrib_location requirements

[Brian Paul]

The spec for GL_ARB_explicit_attrib_location says it requires OpenGL 2.0 
or GL_ARB_vertex_shader and it's written against the OpenGL 3.2 core 
spec / GLSL 1.50.  The extension spec says nothing about how the 
extension would work in GLSL before 1.50.

Note that this extension adds a new layout qualifier, but the "layout" 
keyword/qualifiers were only introduced in GLSL 1.40.

nvidia's failing quite a few of the tests for this extension because 
they only support it in GLSL 1.50 and later.  Many of the tests pass w/ 
nvidia's driver if I add "#version 150" to the top of the shaders.

But other tests like 
tests/spec/arb_explicit_attrib_location/1.10/compiler/* seem bogus since 
they're adding "layout" and "out" language to GLSL 1.10 which seems like 
a stretch.

I think that there's 3 options here:

1. The spec for GL_ARB_explicit_attrib_location should clearly explain 
how things should work with GLSL 1.10, 1.20, 1.30.

2. Some of the piglit tests are invalid.

3. nvidia's driver is incorrect.

I'm leaning toward option 2.

Comments?

-Brian