arb_framebuffer_srgb/blit: check requested samples against GL_MAX_SAMPLES

We can't run some of tests if we don't support multisampling.  Just skip
those tests.

Fixes http://bugs.freedesktop.org/show_bug.cgi?id=60044
framebuffer-srgb: minor comment fix-ups
generated_tests: fix comment errors (int->float, ivec->vec)
tests/es3conform.tests: run GTF for GLES3 tests

[jordan.l.justen@intel.com: use -minfmt rather than -id=77]
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Test varying structs in GLSL ES 3.00.

This patch adds the following GLSL ES 3.00 tests:

- varying-struct-basic: a simple test case involving a single varying
  struct.

- varying-struct-arrays: exercise complex interactions between structs
  and arrays in varyings.

- varying-struct-copy-{function,local}-vs: exercise corner cases where
  a struct internal to a vertex shader is copied to a varying struct.

- varying-struct-copy-{local,out,return,uniform}-fs: exercise corner
  cases where a varying struct is copied to a struct internal to a
  fragment shader.

- varying-struct-interpolation: verify that interpolation qualifiers
  "flat" and "smooth" are inherited by the fields within a varying
  struct.

- varying-struct-centroid: verify that the interpolation qualifier
  "centroid" is inherited by the fields within a varying struct.

Note that "centroid" is tested separately from the other interpolation
qualifiers since MSAA is required to verify that it works correctly,
so it can't be tested with a simple shader_runner test.

v2: Split varying-struct-copy-vs and varying-struct-copy-fs into
sub-tests.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
WIP: varying struct xfb: basic-struct errors
WIP: varying struct xfb: basic-struct get
WIP: varying struct xfb: basic struct run
WIP: varying struct xfb: basic-struct run-no-fs
WIP: varying struct xfb: struct-whole-array
WIP: varying struct xfb: struct-array-elem
WIP: varying struct xfb: array-struct
WIP: varying struct xfb: array-struct-whole-array
WIP: varying struct xfb: array-struct-array-elem
WIP: varying struct xfb: struct-struct
WIP: varying struct xfb: array-struct-array-struct
Add transform feedback struct tests to all.tests, including not-yet-written desktop tests
WIP: 1.50 fixes
WIP: test interface blocks
Whoops, screwed up the get test for interface blocks