Merge branch '4.4'

* 4.4:
  Revert "feature #34329 [ExpressionLanguage] add XOR operator (ottaviano)"
  Allow \Throwable $previous everywhere

Author: nicolas-grekas

Exception/FileNotFoundException.php

@@ -19,7 +19,7 @@
  */
 class FileNotFoundException extends IOException
 {
-    public function __construct(string $message = null, int $code = 0, \Exception $previous = null, string $path = null)
+    public function __construct(string $message = null, int $code = 0, \Throwable $previous = null, string $path = null)
     {
         if (null === $message) {
             if (null === $path) {

Exception/IOException.php

@@ -22,7 +22,7 @@ class IOException extends \RuntimeException implements IOExceptionInterface
 {
     private $path;
 
-    public function __construct(string $message, int $code = 0, \Exception $previous = null, string $path = null)
+    public function __construct(string $message, int $code = 0, \Throwable $previous = null, string $path = null)
     {
         $this->path = $path;