Move loading of user data to authenticator modules

The authenticator modules now load the user data when the new loadusers
entry point is called. This new entry point is optional.

At the moment the code that was in service.c was just moved into the
modules but the ground work for allowing different user loading mechanisms
is done.

Further improvements need to be made so that the authenticators behave
more like routers and filters. This work includes the creation of a
AUTHENTICATOR module object, addition of createInstance entry points for
authenticators and implementing it for all authenticators.

server/include/users.h

@@ -14,6 +14,7 @@
  */
 #include <hashtable.h>
 #include <dcb.h>
+#include <listener.h>
 #include <openssl/sha.h>
 
 /**
@@ -64,6 +65,8 @@ extern int users_delete(USERS *, char *);         /**< Delete a user from the us
 extern char *users_fetch(USERS *, char *);        /**< Fetch the authentication data for a user */
 extern int users_update(USERS *, char *, char *); /**< Change the password data for a user in
                                                      the users table */
+extern int users_default_loadusers(SERV_LISTENER *port); /**< A generic implementation of the authenticator
+                                                          * loadusers entry point */
 extern void usersPrint(USERS *);                  /**< Print data about the users loaded */
 extern void dcb_usersPrint(DCB *, USERS *);       /**< Print data about the users loaded */