Rename option captcha to captcha_protected for consistency

doc/guide.tex

@@ -3792,6 +3792,8 @@ Options:
   doesn't allow to register new accounts from s2s or existing c2s sessions. You can
   change it by defining access rule in this option. Use with care: allowing registration
   from s2s leads to uncontrolled massive accounts creation by rogue users.
+\titem{\{captcha\_protected, false|true\}} \ind{options!captcha\_protected}
+  Protect registrations with CAPTCHA (see section \ref{captcha}). The default is \term{false}.
 \titem{\{welcome\_message, Message\}} \ind{options!welcomem}Set a welcome message that
   is sent to each newly registered account. The first string is the subject, and
   the second string is the message body.

src/mod_register.erl

@@ -96,7 +96,7 @@ process_iq(From, To,
 	   #iq{type = Type, lang = Lang, payload = SubEl, id = ID} = IQ_Rec,
 	   Source) ->
     IsCaptchaEnabled = case gen_mod:get_module_opt(
-			      exmpp_jid:domain(To), ?MODULE, captcha, false) of
+			      exmpp_jid:domain(To), ?MODULE, captcha_protected, false) of
 			   true ->
 			       true;
 			   _ ->