Protect internal services like dbus-daemon and udevd

In f3669c7 the difference between static and dynamic services was
removed.  This led to a regression in handling internally created
services for, e.g., dbus-daemon and udevd, mentioned in issue #90.

This patch introduces a "protected" flag for svc_t to prevent the
mark-and-sweep handling of regularly loaded services.

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

src/service.c

@@ -732,6 +732,9 @@ recreate:
 	else
 		svc_mark_clean(svc);
 
+	if (!file)
+		svc->protected = 1;
+
 	/* Free duped line, from above */
 	free(line);
 	return 0;