_glapi_get_proc_address (and stub_add_dynamic) will now assign an offset to a
new dynamic stub when it's first generated, instead of waiting until
_glapi_add_dispatch.

Deferring it until _glapi_add_dispatch is only useful for handling aliases
(where multiple functions are assigned to the same dispatch table slot), but
libGLdispatch does not use aliases.

Removed the newProcList list in GLdispatch.c. It'll now add all functions
directly to extProcList.

Removed _glapi_add_dispatch and stub_fix_dynamic.