Some shadow fixes.

[Martin v. Loewis]

>   But the problem here is if you do
> 
> #include <stdlib.h>
> #include <math.h>
> 
> because of 7.3.3/9,  if we use a using directive, the abs in math wont be
> visable in the global namespace, or if we swap the inclusion order, vice
> versa (abs is overloaded in both cstdlib and cmath).

Why is that? Both headers contain using std::abs, so all definitions
of std::abs are visible.

Regards,
Martin