Re: undo-auto--undoable-change infloop

[Stefan Monnier]

> I found something in a different place of my code.  That code uses
> `timer-activate', but `timer-activate' doesn't check whether the timer
> is already in the timer list, and that caused the duplicates I think.  I
> didn't expect it to not check that.  Maybe that's the whole story
> already.

I suspect that `timer-activate` was not intended to be used by
end-users, but in any case I added a check that signals an error if you
try to re-add a timer.
[ It would have been better to report this as a bug, so we'd have
  a bug-number to refer to.  ]


        Stefan