a more human warning on php method name mismatch

php/Exchange.php

@@ -1769,7 +1769,7 @@ public function __call ($function, $params) {
             return call_user_func_array ($this->$function, $params);
         else {
             /* handle errors */
-            throw new ExchangeError ($function . ' not found');
+            throw new ExchangeError ($function . ' method not found, try underscore_notation instead of camelCase for the method being called');
         }
     }