DragonFlyBSD

Include alias "args" to /bin/ps as in

ps -o args=MOM

This an alias for command and is required by SUSv3. Also improve argument handling by allowing alternative or empty headings, for example,

ps -o args=

This will make some ports happier (gdm start script stops complaining; passes www/node test-setproctitle).

Changes obtained from OpenBSD bin/ps/keyword.c.