Merge branch '5.1' into 5.x

* 5.1:
  fix merge
  [appveyor] fix checking for the .x branch
  Remove "branch-alias", populate "version"

Author: nicolas-grekas

composer.json

@@ -26,10 +26,5 @@
             "/Tests/"
         ]
     },
-    "minimum-stability": "dev",
-    "extra": {
-        "branch-alias": {
-            "dev-master": "5.2-dev"
-        }
-    }
+    "minimum-stability": "dev"
 }