Hello all,

I've run into this issue today when loading up undo-tree on Emacs 26.1.
The last patch fixes it for me, I only had to delete the first context
line of hunk #13 for it to apply with some fuzz.  I expect plenty more
people to run into this as undo-tree is a dependency for Evil and
therefore keeps Emacs users from properly booting their editor (it's
particularly fatal for the daemon, I couldn't get `emacsclient` to
successfully connect to it after it ran into the issue).

Vasilij