CL: Add int* vload*(constant/local/private) tests

Only tests integer loads, and assumes that global vstore works correctly.

Signed-off-by: Aaron Watry <awatry@gmail.com>
Reviewed-by: Tom Stellard <thomas.stellard@amd.com>
glsl-1.50 compiler: Test that gl_FragCoord redeclaration recognized by compiler

V2: adjusted format and comments for consistency and embarassing typo
GL 3.2: Test for INVALID_ENUM when DrawBuffers() is passed incorrect color buffers

Reviewed-by: Paul Berry <stereotype441@gmail.com>
GL 3.2: Test that Clear() clears no buffers when passed a value of 0

Reviewed-by: Paul Berry <stereotype441@gmail.com>
GL 3.2: Add test for minimum value of MAJOR_VERSION

Reviewed-by: Paul Berry <stereotype441@gmail.com>
Add draw-buffers-errors and clear-no-buffers to all.tests
arb_shading_language_420pack: Don't use const with out or inout parameters

The GLSL 4.40 spec still says:

    "The const qualifier cannot be used with out or inout, or a
    compile-time error results."

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Add PIGLIT_FORCE_WINDOW environment variable.

Setting PIGLIT_FORCE_WINDOW=1 causes all piglit windowsystem tests
(those that weren't invoked with the "-fbo" flag) to show the window
prior to calling piglit_display().  Setting PIGLIT_FORCE_WINDOW=0 (the
default) preserves piglit's existing behaviour, which is to only show
the window when the test is run in "manual" mode (with no "-auto"
argument supplied).

Setting PIGLIT_FORCE_WINDOW=1 slows down the piglit run, and produces
more annoying windows on the screen, but it has been observed to
produce more repeatable results when testing with the nVidia
proprietary driver for Linux.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
ARB_texture_gather: add initial execution test

This test exercises combinations of:
- Shader stage vs/fs
- Offsetting
- Component count, up to implementation-defined limit
- Swizzling
- Unsigned normalized vs float type

The test works by numbering the texels, and ensuring that the four
texels sampled by textureGather*() are those we expect.

Not exercised yet:
- Integer textures
- Samplers other than sampler2D
- Other interesting internalformats [DEPTH_COMPONENT, etc]
- Addressing modes other than WRAP.

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