help.c: wrap wait-only poll() invocation in sleep_millisec()

We want to use the new function elsewhere in a moment.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>
Reviewed-by: Michael Haggerty <mhagger@alum.mit.edu>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

wrapper.c

@@ -595,3 +595,8 @@ int write_file(const char *path, int fatal, const char *fmt, ...)
 	}
 	return 0;
 }
+
+void sleep_millisec(int millisec)
+{
+	poll(NULL, 0, millisec);
+}