glsl: Clean up shading language mixing check for GLSL 3.00 ES.

glsl: Clean up shading language mixing check for GLSL 3.00 ES.

Previously, we prohibited mixing of shading language versions if
min_version == 100 or max_version >= 130.  This was technically
correct (since desktop GLSL 1.30 and beyond prohibit mixing of shading
language versions, as does GLSL 1.00 ES), but it was confusing.  Also,
we asserted that all shading language versions were between 1.00 and
1.40, which was unnecessary (since the parser already checks shading
language versions) and doesn't work for GLSL 3.00 ES.

This patch changes the code to explicitly check that (a) ES shaders
aren't mixed with desktop shaders, (b) shaders aren't mixed between ES
versions, and (c) shaders aren't mixed between desktop GLSL versions
when at least one shader is GLSL 1.30 or greater.  Also, it removes
the unnecessary assertion.

[v2, idr]: Slightly tweak the is_es_prog detection to occur outside the loop
instead of doing something special on the first loop iteration.  Suggested by
Ken.

[v3, idr]: s/IsEs(Shader|Prog)/IsES/  Suggested by Ken and Eric.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com> [v1]
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Carl Worth <cworth@cworth.org>