Issue #223: add type:forking service option, with updated docs

- Add `type:forking` service option to trigger guessing pidfile to
   watch for, instead of `pid:!foo` option, which is not intuitive.
   This option may likely also survive into the new file format :)
 - Update docs and add examples
 - Update start-stop-serv.sh test case with this new variant

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

src/pid.c

@@ -158,6 +158,11 @@ int pid_file_set(svc_t *svc, char *file, int not)
 		file++;
 	}
 
+	if (svc_is_forking(svc) && !not) {
+		logit(LOG_WARNING, "Service %s is forking, adjusting to pid:!%s", svc->name, file);
+		not = 1;
+	}
+
 	pid_runpath(file, &svc->pidfile[not], sizeof(svc->pidfile) - not);
 	if (not)
 		svc->pidfile[0] = '!';