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/Makefile

@@ -1,7 +1,7 @@
 MAN3=		einfo.3 \
 		rc_config.3 rc_deptree.3 rc_find_pids.3 rc_plugin_hook.3 \
 		rc_runlevel.3 rc_service.3 rc_stringlist.3
-MAN8=		rc-service.8 rc-status.8 rc-update.8 rc.8 runscript.8 \
+MAN8=		rc-service.8 rc-status.8 rc-update.8 openrc.8 runscript.8 \
 		service.8 start-stop-daemon.8
 
 # Handy macro to create symlinks