I'm comparing GL function loading libraries, and glbinding looks promising. However, I've had problems with other loader libraries (specifically glLoadGen) not being able to load extension functions in OpenGL versions lower than 3.0 due to vagaries of GL versioning. Does glbinding have this problem?
Actually, glbinding doesn't care whether a function pointer comes from an extension or not. There are two modes how to resolve OpenGL function pointers with glbinding. The first (and default) is to resolve all function pointers at once, which will include every function pointer back to OpenGL 1.0 including all extensions that are available in the current active context. The second is to resolve function pointers with their first use and comes with the same characteristics.
Maybe you speak of querying the list of available extensions, which glbinding currently supports with an OpenGL 3.0 context or newer. The query of extensions for the older versions still needs to be done (thanks for pointing this out, issue is created: https://github.com/hpicgs/glbinding/issues/46).