Prepare for 5.2.0 release

This should be compared to 8e0b7b20 in master, which shows that
this is essensially trunk, but with a different history.

configure.ac

@@ -2,7 +2,7 @@ AC_PREREQ(2.59)
 AC_COPYRIGHT([Copyright (c) 2006 Verdens Gang AS
 Copyright (c) 2006-2017 Varnish Software])
 AC_REVISION([$Id$])
-AC_INIT([Varnish], [5.2.0-rc2], [varnish-dev@varnish-cache.org])
+AC_INIT([Varnish], [5.2.0], [varnish-dev@varnish-cache.org])
 AC_CONFIG_SRCDIR(include/miniobj.h)
 AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])

doc/changes.rst

-=============================
-Varnish Cache Trunk (ongoing)
-=============================
-
 ================================
 Varnish Cache 5.2.0 (2017-09-15)
 ================================