reduce minimum GL version for GLSL 1.30 to GL2.1

Everything in GLSL 1.30 can be usefully supported on a pre-GL3
implementation if we also have EXT_gpu_shader4 to provide the
otherwise GL3+ entrypoints.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
shader_runner: allow unsigned uniforms without GL3

If EXT_gpu_shader4 is supported, we have the GL entrypoints
required.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
isinf/isnan: Relax GL version requirement

This test can work with 2.1 + GLSL 1.30 + EXT_gpu_shader4.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
glsl-1.30: Relax GL version requirement on shader tests

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>
piglit-vbo: allow int attributes without GL3

The required entrypoints for this exist in EXT_gpu_shader4 as well.

Signed-off-by: Chris Forbes <chrisf@ijw.co.nz>