general cleanup: rm unused config.h, add license info to device.c/h, add a couple compiler options and fix warnings

src/dns.c

@@ -20,10 +20,6 @@
  *
  */
 
-#ifdef HAVE_CONFIG_H
-#include "config.h"
-#endif
-
 #include <stdlib.h>
 #include <string.h>
 #include <netinet/in.h>
@@ -284,6 +280,7 @@ void *dns3_lookup_thread(void *data)
     pthread_mutex_unlock(&dns_thread.lock);
 
     kill_dns_thread(dns_obj);
+    return 0;
 }
 
 /* creates new thread for dns3 lookup. Only allows one lookup at a time. */