Merge branch '2.7' into 2.8

* 2.7:
  [HttpFoundation] Use UPSERT for sessions stored in PgSql >= 9.5
  [Console] fixed PHPDoc
  [travis] HHVM 3.12 LTS
  Fix feature detection for IE
  [Form] Fixed collapsed choice attributes
  [Console] added explanation of messages usage in a progress bar
  force enabling the external XML entity loaders
  [Yaml] properly count skipped comment lines

Conflicts:
	src/Symfony/Component/Translation/Loader/XliffFileLoader.php

Author: nicolas-grekas

Resources/views/Profiler/base_js.html.twig

@@ -211,7 +211,7 @@
         var addEventListener;
 
         var el = document.createElement('div');
-        if (!'addEventListener' in el) {
+        if (!('addEventListener' in el)) {
             addEventListener = function (element, eventName, callback) {
                 element.attachEvent('on' + eventName, callback);
             };