Implement UTF-8-clean window titles

include/util.h

@@ -34,6 +34,7 @@ void *scalloc(size_t size);
 char *sstrdup(const char *str);
 void start_application(const char *command);
 void check_error(xcb_connection_t *conn, xcb_void_cookie_t cookie, char *err_message);
+char *convert_utf8_to_ucs2(char *input, int *real_strlen);
 void remove_client_from_container(xcb_connection_t *conn, Client *client, Container *container);
 void set_focus(xcb_connection_t *conn, Client *client);
 void leave_stack_mode(xcb_connection_t *conn, Container *container);