Allow SAMPLE_BINDING snapshot if ARB_sampler_objects extension supported

This fixes a trimming bug on Intel MESA. SAMPLE_BINDING was not being captured b/c Mesa currently only GL 3.0 and SAMPLE_BINDING is 3.3.  However, Intel MESA supports ARB_sampler_objects extension so with this change it will now capture SAMPLE_BINDING state.
Merge pull request #158 from tobin-lunarg/intc_trim_fix

Allow SAMPLE_BINDING snapshot if ARB_sampler_objects extension supported