Merge branch '3.4' into 4.4

* 3.4:
  [Filesystem] Handle paths on different drives
  [WebProfiler] Do not add src-elem CSP directives if they do not exist
  [Yaml] fix parse error when unindented collections contain a comment
  [3.4][Inflector] Improve testSingularize() argument name
  [PhpUnitBridge] fix PHP 5.3 compat again
  Skip validation when email is an empty object
  fix sr_Latn translation
  [Validator] fix lazy property usage.
  Fix annotation
  [PhpUnitBridge] fix compat with PHP 5.3
  [DX] Show the ParseException message in YAML file loaders

Author: nicolas-grekas

Loader/YamlFileLoader.php

@@ -62,7 +62,7 @@ public function load($file, $type = null)
         try {
             $parsedConfig = $this->yamlParser->parseFile($path, Yaml::PARSE_CONSTANT);
         } catch (ParseException $e) {
-            throw new \InvalidArgumentException(sprintf('The file "%s" does not contain valid YAML.', $path), 0, $e);
+            throw new \InvalidArgumentException(sprintf('The file "%s" does not contain valid YAML', $path).': '.$e->getMessage(), 0, $e);
         }
 
         $collection = new RouteCollection();