Conditionally add options to unserialize in PHP 7.0+.

Author: Denis Brumann

FormError.php

@@ -185,6 +185,10 @@ public function serialize()
      */
     public function unserialize($serialized)
     {
-        list($this->message, $this->messageTemplate, $this->messageParameters, $this->messagePluralization, $this->cause) = unserialize($serialized);
+        if (PHP_VERSION_ID >= 70000) {
+            list($this->message, $this->messageTemplate, $this->messageParameters, $this->messagePluralization, $this->cause) = unserialize($serialized, array('allowed_classes' => false));
+        } else {
+            list($this->message, $this->messageTemplate, $this->messageParameters, $this->messagePluralization, $this->cause) = unserialize($serialized);
+        }
     }
 }