New function: Exchange parameter array in ParamBag

* VuFindSearch/ParamBag.php (exchangeArray): New function. Exchange
  parameter array.

module/VuFindSearch/src/VuFindSearch/ParamBag.php

@@ -192,6 +192,20 @@ class ParamBag
         return $this->params;
     }
 
+    /**
+     * Exchange the parameter array.
+     *
+     * @param array $input New parameters
+     *
+     * @return array Old parameters
+     */
+    public function exchangeArray(array $input)
+    {
+        $current = $this->params;
+        $this->params = $input;
+        return $current;
+    }
+
     /**
      * Return array of params ready to be used in a HTTP request.
      *