[4.1] 1479325 Add req_top to the list of changes.

[Lasse Karstensen]

commit 14793254fb0281e86f1f17da9b30b6946ee1d872
Author: Lasse Karstensen <lkarsten at varnish-software.com>
Date:   Fri Jul 31 11:35:53 2015 +0200

    Add req_top to the list of changes.

diff --git a/doc/sphinx/whats-new/changes.rst b/doc/sphinx/whats-new/changes.rst
index 2dd4a16..b7fd4da 100644
--- a/doc/sphinx/whats-new/changes.rst
+++ b/doc/sphinx/whats-new/changes.rst
@@ -102,6 +102,16 @@ Surrogate keys
 
 Not yet documented.
 
+Passing data between ESI requests
+=================================
+
+A new `req_top` identifier is available in VCL, which is a reference
+to `req` in the top-level ESI request.
+
+This is useful to pass data back and forth between the main ESI request
+and any ESI subrequests it lead to.
+
+
 Other noteworthy small changes
 ==============================