Various Changes to OpenGL intialization

I removed all extension checking code to gl-subsystem.c as it needs to be called on all platforms and does not change given a platform. 
I added a function and tables to handle OpenGL debug and error messages via the ARB_debug_output extension or via the GL 4.0 API if available. 
I removed the hardcoded request for a 3.2 context on Linux and Windows. It will now give the latest context given it fits our requirements (which is just a core profile and debug context if _DEBUG is set currently). 

Snuck in was a change to autoconf that allows autoconf to correctly find wxWidgets 2.9 (or greater) with wx-config (not just wx-config-2.9) without user interaction.