Merge branch '3.4' into 4.0

* 3.4:
  Have weak_vendors ignore deprecations from outside
  [HttpFoundation] fixed return type of method HeaderBag::get
  [HttpFoundation] Added "resource" type on Request::create docblock
  [Process] Skip environment variables with false value in Process
  Revert "bug #25789  Enableable ArrayNodeDefinition is disabled for empty configuration (kejwmen)"
  Formatting fix in upgrade 3.0 document
  don't split lines on carriage returns when dumping
  Revert "bug #25851 [Validator] Conflict with egulias/email-validator 2.0 (emodric)"
  [DI] compilation perf tweak
  [Validator] Conflict with egulias/email-validator 2.0
  [Validator] add missing parent isset and add test

Author: nicolas-grekas

Compiler/AbstractRecursivePass.php

@@ -52,7 +52,7 @@ public function process(ContainerBuilder $container)
      */
     protected function processValue($value, $isRoot = false)
     {
-        if (is_array($value)) {
+        if (\is_array($value)) {
             foreach ($value as $k => $v) {
                 if ($isRoot) {
                     $this->currentId = $k;