We would need to use `'equal` for comparison, but Emacs 25 only allows `'eq`.
Using `advice-add` to override `alist-get` does not work, because `setf`
has special handling for `alist-get`.
`repl.el`: Switch to a hash table which already supports multiple comparison
functions, and changing of elements even in Emacs 25.
`eshell/autoload/settings.el`: use conditional set-or-push.
Drop `doom*alist-get`, it is unused now.
Thanks to @hlissner for the reimplementation.
b9c966ec54