Timothy Arceri posted his full patch-set today to Mesa-dev for implementing KHR_debug, the OpenGL extension that's required as of version 4.2 and used for assisting in GL debugging. The specification is outlined at OpenGL.org for those interested in the finer details.
The developer raised $3,205 of his $2,500 goal for being able to focus two weeks on learning Mesa and implementing this GL4 extension. In his remaining four days on the work he's planning to working on more documentation and cleaning up the code further. Additional details on the GL_KHR_debug work can be found on his GitHub Wiki.