Interface update

All of the OpenGL interface should now be present (symbols for 1 or 2 minor versions were missing before).
Automatic error checking has been added, and is enabled by default. This seems like a reasonable change, but it's possible to omit any additional code by defining NoGlAutoErrorCheck. enableGlAutoErrorCheck(bool) can be used to control this at run time, provided that NoGlAutoErrorCheck hasn't been defined.

I'll be documenting these changes soon.