Have not come up with a great pattern for flock() yet. flock() is permitted

Have not come up with a great pattern for flock() yet.  flock() is permitted
by "getpw" because libc getpw*/getgr* use open() of /var/run/ypbind.lock plus
flock() to detect YP running.  The kernel observes this dance to "open up" the
YP door (ugliness should drive us to rewrite this mechanism from SunOS later).

however, flock is also used independently.  Current users are
    htpasswd mail skeyinit tmux authpf pwd_mkdb ldapd smtpd ypbind
    login_token mail.local lockspool
Let's enable flock() for "cpath", and see if that helps these programs,
otherwise we'll try "wpath" next.