Merge pull request #3985 from owncloud/cookie-past2

apply @LukasReschke's cookie changes, hopefully finally fix #854

lib/user/session.php

@@ -166,8 +166,8 @@ class Session implements Emitter {
 		unset($_COOKIE["oc_username"]); //TODO: DI
 		unset($_COOKIE["oc_token"]);
 		unset($_COOKIE["oc_remember_login"]);
-		setcookie("oc_username", null, -1);
-		setcookie("oc_token", null, -1);
-		setcookie("oc_remember_login", null, -1);
+		setcookie('oc_username', '', time()-3600, \OC::$WEBROOT);
+		setcookie('oc_token', '', time()-3600, \OC::$WEBROOT);
+		setcookie('oc_remember_login', '', time()-3600, \OC::$WEBROOT);
 	}
 }