[RFC] vim-patch:7.4.414 + vim-patch:7.4.415

> Problem:    Cannot define a command only when it's used.

> Solution:   Add the CmdUndefined autocommand event. (partly by Yasuhiro Matsumoto)

That's 414--415 is a fixup. Also reformatted `fileio.c`'s diagram, which looks wrong if `tabstop` isn't 4.