[resend] sxs: Implement SxsLookupClrGuid and add tests

[Fabian Maurer]

> > +    pSxsLookupClrGuid = (void *)GetProcAddress(LoadLibraryA("sxs.dll"),
> > "SxsLookupClrGuid");
> Is there a reason you are not linking to it directly?

Actually, no there's not - I can change that. Is the rest of the patch okay?

Regards,
Fabian Maurer