Add in rlimits_maximize_nofiles() to workaround setrlimit() restrictions on macOS.

Rather than repeat the #ifdef block through five locations, use a common
function to handle this and print a consistent error message if there
is an issue.

From getrlimit(2):
	setrlimit() now returns with errno set to EINVAL in places that
	historically succeeded. It no longer accepts "rlim_cur =
	RLIM_INFINITY" for RLIM_NOFILE. Use "rlim_cur = min(OPEN_MAX,
	rlim_max)".

(This was causing spurious error messages to appear for sbatch/srun.)