captcha_host must have the port number to get protocol (EJAB-1418)

doc/guide.tex

@@ -1709,11 +1709,11 @@ The configurable options are:
   \titem{\{captcha\_cmd, Path\}} 
   Full path to a script that generates the image.
   The default value is an empty string: \term{""}
-  \titem{\{captcha\_host, Host\}} 
-  Host part of the URL sent to the user.
-  You can include the port number.
-  The URL sent to the user is formed by: \term{http://Host/captcha/}
-  The default value is the first hostname configured.
+  \titem{\{captcha\_host, HostPort\}} 
+  Host part of the URL sent to the user,
+  and the port number where ejabberd listens for CAPTCHA requests.
+  The URL sent to the user is formed by: \term{http://Host:Port/captcha/}
+  The default value is: the first hostname configured, and port 5280.
 \end{description}
 
 Additionally, an \term{ejabberd\_http} listener must be enabled with the \term{captcha} option.

src/ejabberd.cfg.example

@@ -480,8 +480,7 @@
 %%
 %%{captcha_cmd, "/lib/ejabberd/priv/bin/captcha.sh"}.
 
-%%
-%% Host part of the URL sent to the user.
+%% Host for the URL and port where ejabberd listens for CAPTCHA requests.
 %%
 %%{captcha_host, "example.org:5280"}.
 

src/ejabberd_captcha.erl

@@ -626,12 +626,12 @@ get_prog_name() ->
 %% @doc (Str::string()) -> string()
 get_url(Str) ->
     CaptchaHost = ejabberd_config:get_local_option(captcha_host),
-    TransferProt = atom_to_list(get_transfer_protocol(CaptchaHost)),
     case CaptchaHost of
 	Host when is_list(Host) ->
+	    TransferProt = atom_to_list(get_transfer_protocol(CaptchaHost)),
 	    TransferProt ++ "://" ++ Host ++ "/captcha/" ++ Str;
 	_ ->
-	    TransferProt ++ "://" ++ ?MYNAME ++ "/captcha/" ++ Str
+	    "http://" ++ ?MYNAME ++ ":5280/captcha/" ++ Str
     end.
 
 get_transfer_protocol(CaptchaHost) ->