ediff-mode should be in emacs state

[York Zhao]

> And some more (sorry for the trickling):
>
> - slime-xref-mode
> - slime-inspector-mode
> - slime-thread-control-mode
>

Hi Michael,

I'm impressed that you seemed to know a bunch of emacs mode which is good and I
think you must have been using emacs for a long time. So among the
modes you have
suggested adding to emacs state so far, which one do you like the best
or you think
really useful?

Thanks,

York