Really protect against unwanted indentation after undo

When I am undoing changes to a region I really want the changes to be
undone verbatim, that is, I want the buffer's contents to be like they
were before the change that I want to undo occured.  This is the very
definition of undo.

It is probably the rationale for giving undo special treatment in
aggressive-indent--internal-dont-indent-if in the first place.  It
means that the undo command won't immediately cause reindentation.

But it doesn't fix the whole problem, because changes performed by
undo itself are still recorded into aggressive-indent--changed-list
and the very next command, be it a move or an edit somewhere else,
will still cause those regions to be indented.  Among other things,
it's impossible in practice to use `undo' to undo an aggressive indent
of a region.

The proposed fix checks adds a function to the post-command hook to
check for aggressive-indent-protected-commands and clear the change
list if the current command is in that list.  This is safe if those
changes can only have been performed by the command whose
auto-indentation effects we want to prevent.

* aggressive-indent.el (aggressive-indent--keep-track-of-changes):
Check undo-in-progress.

* aggressive-indent.el
(aggressive-indent--internal-dont-indent-if): Remove check of
aggressive-indent-protected-commands and undo-in-progress.
(aggressive-indent--post-command): New helper.
(aggressive-indent-mode): Put aggressive-indent--post-command in
post-command-hook and remove it when exiting minor mode.

aggressive-indent.el

@@ -167,11 +167,9 @@ change."
 
 ;;; Preventing indentation
 (defconst aggressive-indent--internal-dont-indent-if
-  '((memq last-command aggressive-indent-protected-commands)
-    (memq this-command aggressive-indent-protected-current-commands)
+  '((memq this-command aggressive-indent-protected-current-commands)
     (region-active-p)
     buffer-read-only
-    undo-in-progress
     (null (buffer-modified-p))
     (and (boundp 'smerge-mode) smerge-mode)
     (equal (buffer-name) "*ediff-merge*")
@@ -471,6 +469,15 @@ If BODY finishes, `while-no-input' returns whatever value BODY produced."
       (when (timerp aggressive-indent--idle-timer)
         (cancel-timer aggressive-indent--idle-timer)))))
 
+(defun aggressive-indent--post-command ()
+  "Hook run after every command while in `aggressive-indent-mode'.
+
+Clears `aggressive-indent--changed-list' iff the current
+command (the one that's now finished) lives in
+`aggressive-indent-protected-current-commands'."
+  (when (memq this-command aggressive-indent-protected-commands)
+    (setq aggressive-indent--changed-list nil)))
+
 (defun aggressive-indent--keep-track-of-changes (l r &rest _)
   "Store the limits (L and R) of each change in the buffer."
   (when aggressive-indent-mode
@@ -509,14 +516,15 @@ If BODY finishes, `while-no-input' returns whatever value BODY produced."
           (aggressive-indent--local-electric t))
         (add-hook 'after-change-functions #'aggressive-indent--keep-track-of-changes nil 'local)
         (add-hook 'after-revert-hook #'aggressive-indent--clear-change-list nil 'local)
-        (add-hook 'before-save-hook #'aggressive-indent--proccess-changed-list-and-indent nil 'local))
+        (add-hook 'before-save-hook #'aggressive-indent--proccess-changed-list-and-indent nil 'local)
+        (add-hook 'post-command-hook #'aggressive-indent--post-command nil 'local))
     ;; Clean the hooks
     (when (timerp aggressive-indent--idle-timer)
       (cancel-timer aggressive-indent--idle-timer))
     (remove-hook 'after-change-functions #'aggressive-indent--keep-track-of-changes 'local)
     (remove-hook 'after-revert-hook #'aggressive-indent--clear-change-list 'local)
     (remove-hook 'before-save-hook #'aggressive-indent--proccess-changed-list-and-indent 'local)
-    (remove-hook 'post-command-hook #'aggressive-indent--softly-indent-defun 'local)))
+    (remove-hook 'post-command-hook #'aggressive-indent--post-command 'local)))
 
 (defun aggressive-indent--local-electric (on)
   "Turn variable `electric-indent-mode' on or off locally, as per boolean ON."