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

Store/FlockStore.php

@@ -79,12 +79,12 @@ private function lock(Key $key, $blocking)
 
         // Silence error reporting
         set_error_handler(function ($type, $msg) use (&$error) { $error = $msg; });
-        if (!$handle = fopen($fileName, 'r')) {
+        if (!$handle = fopen($fileName, 'r+') ?: fopen($fileName, 'r')) {
             if ($handle = fopen($fileName, 'x')) {
                 chmod($fileName, 0444);
-            } elseif (!$handle = fopen($fileName, 'r')) {
+            } elseif (!$handle = fopen($fileName, 'r+') ?: fopen($fileName, 'r')) {
                 usleep(100); // Give some time for chmod() to complete
-                $handle = fopen($fileName, 'r');
+                $handle = fopen($fileName, 'r+') ?: fopen($fileName, 'r');
             }
         }
         restore_error_handler();