st/wgl: Don't return core profile for 3.1 contexts.

st/wgl: Don't return core profile for 3.1 contexts.

WGL_CONTEXT_PROFILE_MASK_ARB doesn't apply to desktop OpenGL versions
less than 3.2 -- applications can't specify whether they want a core or
a compat 3.1 context -- instead they are supposed the check whether the
returned context advertises GL_ARB_compatibility extension.

Mesa doesn't support compatability contexts for version higher than 3.1,
so we used to return core profile context, but this makes several Windows
applications unhappy, because they just assume they got a compatability
context without checking.

So it seems safer to on Windows to never return core profile for 3.1,
ie, just fail the context creation.

VMware PR1365920.

Reviewed-by: Brian Paul <brianp@vmware.com>