MINOR: config: make str2listener() use memprintf() to report errors.

This will make it possible to use the function for other listening
sockets.
diff --git a/include/common/cfgparse.h b/include/common/cfgparse.h
index e7ba8d1..dcc4003 100644
--- a/include/common/cfgparse.h
+++ b/include/common/cfgparse.h
@@ -69,6 +69,7 @@
 void cfg_unregister_keywords(struct cfg_kw_list *kwl);
 void init_default_instance();
 int check_config_validity();
+int str2listener(char *str, struct proxy *curproxy, struct bind_conf *bind_conf, const char *file, int line, char **err);
 
 #endif /* _COMMON_CFGPARSE_H */