!UPSTREAM: GS: gl_ClipDistanceIn tests

TODO:
- Commit message
- Validate on nVidia
glslparsertest: Fix handling of GL_GEOMETRY_VERTICES_OUT_ARB.

When testing geometry shaders, glslparsertest must set
GL_GEOMETRY_VERTICES_OUT_ARB before linking, since the default value
of this setting (0) is fairly useless.

Previously, we were accidentally passing the shader name to
glProgramParameteri() instead of the program name, causing spurious
errors.