Remove debug message when debugging is disabled

Long description:

More precisely, switch from printf to DLOG a "matching: * / *" message, like all
the other "matching: * / *" messages.

To apply this patch, use:
curl http://cr.i3wm.org/patch/205/raw.patch | git am

@@ -1521,7 +1521,7 @@ void cmd_fullscreen(I3_CMD, char *fullscreen_mode) {

     HANDLE_EMPTY_MATCH;

     TAILQ_FOREACH(current, &owindows, owindows) {

-        printf("matching: %p / %s\n", current->con, current->con->name);

+        DLOG("matching: %p / %s\n", current->con, current->con->name);

         con_toggle_fullscreen(current->con, (strcmp(fullscreen_mode, "global") == 0 ? CF_GLOBAL : CF_OUTPUT));

     }