[Ur] openid fails to build on OS X

[Adam Chlipala]

austin seipp wrote:
> Here's a version that produces predictable results:
>
> uw_Basis_bool uw_OpenidFfi_secCmp(uw_context ctx, uw_Basis_string s1,
> uw_Basis_string s2) {
>    int i, x = 0, len1 = strlen(s1);
>    if (len1 != strlen(s2)) return 0;
>    for (i = 0; i<  len1; ++i) {
>          __asm__ __volatile__ ("");
>          x |= s1[i] ^ s2[i];
>    }
>    return x == 0;
> }
>    

I've added that version to the base Ur/Web distribution, since there's 
comparison of cryptographic signatures there too, and I've changed the 
openid library to call that function.  Thanks for you research on this!