Make list-commands command show only one command if an argument is

given, from Ilya Grigoriev in GitHub issue 4352.

cmd.c

@@ -445,7 +445,7 @@ cmd_get_alias(const char *name)
 }
 
 /* Look up a command entry by name. */
-static const struct cmd_entry *
+const struct cmd_entry *
 cmd_find(const char *name, char **cause)
 {
 	const struct cmd_entry	**loop, *entry, *found = NULL;