specs: Fix GL_ARB_robustness/GL_KHR_robustness spec.
specs: Fix GL_ARB_robustness/GL_KHR_robustness spec.

bufsize is in bytes.  And we were missing a few GL_KHR_robustness
entrypoints.

apitrace/apitrace,apitrace/apitrace,apitrace/apitrace,apitrace/apitrace