Specify the Google Analytics tmp folder

This prevents some errors on shared host and makes use of a known Symphony folder which should be writable.

extension.driver.php

@@ -185,6 +185,7 @@ public function dashboard_panel_validate($context) {
 
 		public static function createClient(array $config, $panelId) {
 			$client = new Google_Client();
+			$client->setClassConfig('Google_Cache_File', 'directory', TMP);
 			$keyfile = $config['keyfile'];
 			if (strpos($keyfile, '/') !== 0) {
 				$keyfile = DOCROOT . '/' . $keyfile;