• Add two new subcommands to rc.subr: "describe" shows an rc script's description "extracommands" shows an rc script's non-standard commands like "reload", "configtest", "keygen", etc
• Update the rc(8) manpage and the tcsh(1) completion examples to reflect these changes

Approved by: bapt
Sponsored by: Essen Linuxhotel Hackathon 2016
Differential Revision: D452