Rename the rc binary to openrc

Debian requested this rename due to the "rc" binary conflicting with the
"rc" binary from the plan 9 shell.

We also add a deprecation warning to the binary when it is run as rc to
encourage users to switch to openrc instead.

X-Gentoo-Bug: 493958
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=493958

man/rc-update.8

@@ -86,7 +86,7 @@ If the
 option is given then we either add or remove the runlevel from the runlevel.
 This allows inheritance of runlevels.
 .Sh SEE ALSO
-.Xr rc 8 ,
+.Xr openrc 8 ,
 .Xr rc-status 8
 .Sh AUTHORS
 .An Roy Marples <roy@marples.name>