[Piglit] [PATCH v3 5/5] arb-enhanced-layouts: explicit-offset piglits

[Emil Velikov]

Hi all,

Updated tests based on the feedback received so far:
 - Dropped trailing white space
 - Change glsl version to 1.40 for the ssbo tests
 - Add check_link true to the compiler tests for compliance with 
official Nvidia driver
 - Test only one thing at a time (some negative tests had two issues)
 - Rework link tests into separate inter/intra stage ones.

Comments and suggestions are appreciated.
Emil