Merge branch '2.8' into 3.4

* 2.8:
  [HttpKernel] fix test compat with PHP 5.3
  fix file lock on SunOS
  change `evaluate()` docblock return type from string to mixed
  Set serialize_precision explicitly to avoid fancy float rounding

Author: nicolas-grekas

LockHandler.php

@@ -81,12 +81,12 @@ public function lock($blocking = false)
             $error = $msg;
         });
 
-        if (!$this->handle = fopen($this->file, 'r')) {
+        if (!$this->handle = fopen($this->file, 'r+') ?: fopen($this->file, 'r')) {
             if ($this->handle = fopen($this->file, 'x')) {
                 chmod($this->file, 0444);
-            } elseif (!$this->handle = fopen($this->file, 'r')) {
+            } elseif (!$this->handle = fopen($this->file, 'r+') ?: fopen($this->file, 'r')) {
                 usleep(100); // Give some time for chmod() to complete
-                $this->handle = fopen($this->file, 'r');
+                $this->handle = fopen($this->file, 'r+') ?: fopen($this->file, 'r');
             }
         }
         restore_error_handler();