Merge branch '4.0' into 4.1

* 4.0:
  [Lock] use 'r+' for fopen (fixes issue on Solaris)
  [HttpKernel] fix test compat with PHP 5.3
  fix handling of nested Error instances
  fix file lock on SunOS
  [Cache] more granular handling of exceptions in AbstractTrait::clear()
  change `evaluate()` docblock return type from string to mixed
  Set serialize_precision explicitly to avoid fancy float rounding

Author: nicolas-grekas

ExpressionLanguage.php

@@ -60,7 +60,7 @@ public function compile($expression, $names = array())
      * @param Expression|string $expression The expression to compile
      * @param array             $values     An array of values
      *
-     * @return string The result of the evaluation of the expression
+     * @return mixed The result of the evaluation of the expression
      */
     public function evaluate($expression, $values = array())
     {