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/floating.c

@@ -15,7 +15,7 @@ extern xcb_connection_t *conn;
  * Calculates sum of heights and sum of widths of all currently active outputs
  *
  */
-Rect total_outputs_dimensions() {
+static Rect total_outputs_dimensions(void) {
     Output *output;
     /* Use Rect to encapsulate dimensions, ignoring x/y */
     Rect outputs_dimensions = {0, 0, 0, 0};