MXS-1758 Support anonymous user with proxy grant for PAM

This allows using user group mapping with PAM authenticator.

server/modules/authenticator/PAM/PAMAuth/pam_instance.hh

@@ -36,6 +36,7 @@ private:
     void add_pam_user(const char *user, const char *host, const char *db, bool anydb,
                       const char *pam_service);
     void delete_old_users();
+    bool query_anon_proxy_user(SERVER* server, MYSQL* conn);
 
     sqlite3 * const m_dbhandle; /**< SQLite3 database handle */
 };