A possible security bug fix

[gwyn at brl-vld]

From:      Doug Gwyn (VLD/VMB) <gwyn at brl-vld>

Yes, there is a problem with requiring FDs 0..2 to be open on exec;
that would keep people from shutting up stderr by
	$ foo 2>&-

Better to write the programs in a paranoid style (check everything that
might go wrong).  Too many UNIX programs fail disastrously when they
could recover from unexpected situations, or at least terminate gracefully.