Merge branch '4.0' into 4.1

* 4.0:
  Remove mentions of "beta" in composer.json files
  bug #27299 [Cache] memcache connect should not add duplicate entries on sequential calls
  simple-phpunit: remove outdated appveryor workaround

Author: nicolas-grekas

composer.json

@@ -41,7 +41,7 @@
         "symfony/security": "~3.4|~4.0",
         "symfony/form": "^4.1",
         "symfony/expression-language": "~3.4|~4.0",
-        "symfony/messenger": "^4.1-beta2",
+        "symfony/messenger": "^4.1",
         "symfony/process": "~3.4|~4.0",
         "symfony/security-core": "~3.4|~4.0",
         "symfony/security-csrf": "~3.4|~4.0",