Implement explicit selection of subsystem types.

- Fixes bugs #347583, #349389, both of which were triggered by cgroups
  being detected as the LXC subsystem type.
- Makes it much easier to select "prefix" type.
- "rc -S" will now print a warning if you have not configured rc_sys in
  /etc/rc.conf
- All other semantics of rc_sys are unchanged in this patch.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

src/rc/rc.c

@@ -878,9 +878,16 @@ main(int argc, char **argv)
 			eerrorx("%s: %s", applet, strerror(errno));
 			/* NOTREACHED */
 		case 'S':
-			bootlevel = rc_sys();
-			if (bootlevel)
-				printf("%s\n", bootlevel);
+			if (rc_conf_value("rc_sys")) {
+				bootlevel = rc_sys_v2();
+				if(bootlevel)
+					printf("%s\n", bootlevel);
+			} else {
+				ewarn("WARNING: rc_sys not defined in rc.conf. Falling back to automatic detection");
+				bootlevel = rc_sys_v1();
+				if(bootlevel)
+					printf("%s\n", bootlevel);
+			}
 			exit(EXIT_SUCCESS);
 			/* NOTREACHED */
 			case_RC_COMMON_GETOPT