Change ps(1) output width to unlimited if not interactive

Apply patch submitted with PR 217159 to make ps use unlimited
width when not associated with a terminal (i.e., none of stdout, stdin,
or stderr is a tty). Update comments and man page correspondingly.
This change was requested to work around lack of -ww in scripts from
third-party packages, including Hadoop, and adds a small measure of
Linux compatibility. Hopefully few if any non-interactive scripts
depend on the old default of 79.

PR: 217159
Submitted by: n.deepak at gmail.com
Reviewed by: vangyzen jhb
Differential Revision: https://reviews.freebsd.org/D14614