When GLSL version 1.30 is supported, transform feedback can output
integral types (uint, int, uvec, and ivec).  This patch expands the
existing EXT_transform_feedback/output-type tests to validate those
integral types.

Verified on the closed-source nVidia Linux driver and on Mesa master
using Intel Sandy Bridge.

Reviewed-by: Eric Anholt <eric@anholt.net>