Use (void) instead of () for functions without args (Thanks fernandotcl)

See also:
http://article.gmane.org/gmane.linux.kernel/1268792

The C compiler will handle (void) as "no arguments" and () as "variadic
function" (equivalent to (...)) which might lead to subtle errors, such
as the one which was fixed with commit 0ea64ae4.

src/ipc.c

@@ -97,7 +97,7 @@ void ipc_send_event(const char *event, uint32_t message_type, const char *payloa
  * when exiting or restarting only!
  *
  */
-void ipc_shutdown() {
+void ipc_shutdown(void) {
     ipc_client *current;
     while (!TAILQ_EMPTY(&all_clients)) {
         current = TAILQ_FIRST(&all_clients);