Add custom headers for test client

Author: manhtai

src/There4/Slim/Test/WebTestClient.php

@@ -86,6 +86,8 @@ private function request($method, $path, $data = array(), $optionalHeaders = arr
         $env = Slim\Environment::getInstance();
         $this->app->router = new NoCacheRouter($this->app->router);
         $this->app->request = new Slim\Http\Request($env);
+        // Custom headers
+        $this->app->request->headers = new Slim\Http\Headers($env);
         $this->app->response = new Slim\Http\Response();
 
         // Establish some useful references to the slim app properties