Added context-creation test to stress test that many contexts can be created without spontaneously failing.
Addressed pull request feedback
Merge pull request #434 from toji/context_creation_2

Added context-creation test
Manual test for leakage.
review fixes.
Merge pull request #436 from baxissimo/instancing-leakage-test

Add a manual conformance test for ANGLE_instanced_arrays state leakage.