bin/150772: csup should include limits.h instead of sys/limits.h

[Bruce Evans]

On Tue, 21 Sep 2010, Derrick Brashear wrote:

>> Description:
> All but one inclusion of limits.h use the portable (/usr/include) header path; One uses sys/limits.h, which is included by limits.h.

I wonder if we could properly break unportable includers.  In this case,
maybe use one of:

A. Don't install <sys/limits.h>.  Requires some reorganization, since
    <limits.h> incudes it now.
B. #error if <sys/limits.h> is included by anything except <limits.h>
    outside of the kernel.

Bruce