MFC r216744 for rc.d/devd:

Add pidfile [1]

While I'm here, don't run the sysctl frob unconditionally, and
s/sysctl/$SYSCTL/

MFC r220962:

Introduce to rc.subr get_pidfile_from_conf(). It does just what it sounds
like, determines the path to a pid file as it is specified in a conf file.

Use the new feature for rc.d/named and rc.d/devd, the 2 services in the
base that list their pid files in their conf files.

Remove the now-obsolete named_pidfile, and warn users if they have it set.

MFC r220963:

Improve the error handling for the new get_pidfile_from_conf()