Correct docs for behaviour of ALTER DATABASE .. RENAME during Hot Standby.

Actual behaviour did not match documented behaviour and we have agreed
that it should be the docs that change.

Spotted by Bernd Helmle

doc/src/sgml/high-availability.sgml

@@ -1764,12 +1764,15 @@ LOG:  database system is ready to accept read only connections
    </para>
 
    <para>
-    Running <command>DROP DATABASE</>, <command>ALTER DATABASE ... SET
-    TABLESPACE</>, or <command>ALTER DATABASE ... RENAME</> on the primary
+    Running <command>DROP DATABASE</> or <command>ALTER DATABASE ... SET
+    TABLESPACE</> on the primary
     will generate a WAL entry that will cause all users connected to that
     database on the standby to be forcibly disconnected. This action occurs
     immediately, whatever the setting of
-    <varname>max_standby_streaming_delay</>.
+    <varname>max_standby_streaming_delay</>. Note that
+    <command>ALTER DATABASE ... RENAME</> does not disconnect users, which
+    in most cases will go unnoticed, though might in some cases cause a
+    program confusion if it depends in some way upon database name.
    </para>
 
    <para>