doc: add downgrade.rst

Author: jengelh

doc/downgrade.rst

@@ -0,0 +1,36 @@
+Running older Gromox version requires extra hoops, documented herein.
+
+Windows must not run in CP_UTF8 mode if going earlier than gromox-2.18.
+
+``/usr/share/gromox/data/http/php/ews`` needs to contain the old
+AutoDiscover implementation.
+
+.. code-block:: sh
+
+	mkdir data/http
+	ln -s ~/gromox/exch/http/ews data/http/ews
+	ln -s ~/gromox/data /usr/share/gromox
+
+``/etc/gromox/autodiscover.ini`` needs to be re-populated:
+
+.. code-block:: text
+
+	[database]
+	host=localhost
+	username=root
+	password=
+	dbname=grommunio
+	[exchange]
+	hostname=a4.inai.de
+	mapihttp=0
+	[system]
+	[http-proxy]
+	/var/lib/gromox/user/ = a4.inai.de
+	/var/lib/gromox/domain/ = a4.inai.de
+
+``/etc/gromox/http.cfg`` needs additional lines:
+
+.. code-block:: text
+
+	listen_ssl_port=443
+	http_support_ssl=on