added redirect::back method.

laravel/request.php

@@ -131,6 +131,16 @@ class Request {
 		return strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) === 'xmlhttprequest';
 	}
 
+	/**
+	 * Get the HTTP referrer for the request.
+	 *
+	 * @return string
+	 */
+	public static function referrer()
+	{
+		return array_get($_SERVER, 'HTTP_REFERER');
+	}
+
 	/**
 	 * Determine if the current request is via the command line.
 	 *