Is it possible to disable this loading of undo-tree history? If so,
can you disable it and see if Emacs no longer crashes? If the crashes
stop when undo-tree history is not loaded, we will have to look
closely at what that loading does, because the problem is probably
there. The internals of undo changed in Emacs 25.
Yes, I know, but that requires me to have an X server here, which I
don't have, and prefer not to set up. Is there some way of telling
Emacs to open its display on your local terminal instead?