[BrowserKit] added the method to Client which enables to set single server parameter

src/Symfony/Component/BrowserKit/Client.php

@@ -108,6 +108,17 @@ abstract class Client
         ), $server);
     }
 
+    /**
+     * Sets single server parameter.
+     *
+     * @param string $key   A key of the parameter
+     * @param string $value A value of the parameter
+     */
+    public function setServerParameter($key, $value)
+    {
+        $this->server[$key] = $value;
+    }
+
     /**
      * Returns the History instance.
      *