Not sure about the extension replacement mechanism. Also, should tests be failing when extensions aren't supported?
-- v2: opengl32: Implement GL_EXT_memory_object_win32 for base handle types. opengl32: Implement GL_DEVICE_LUID_EXT and GL_DEVICE_NODE_MASK_EXT. opengl32: Unify glGet* and fix typo in glGetDoublev.