follow-minor-mode stops working after free motion

[rolandwalker]

From #174 :

After this PR, pygn-mode-follow-minor-mode works correctly, IFF pygn-mode-next-move and pygn-mode-previous-move are used to navigate. But if I move the cursor freely through variations and comments, the "follow" board window eventually stops being updated at all, and the follow mode stops working.

We need to

• find out if this is an old bug, or whether it was introduced by the tree-sitter port
• check whether the recent Greatly simplify pygn-mode-pgn-at-pos using tree-sitter #177 happened to affect it
• track down the problem and fix

[dekrueger]

I added the above commit to get following semi-working. It still doesn't function in variations, probably due to errors in pgn-at-pos-as-if-variation. I tried to be expansive in the commit message. Hopefully it can help you track down this issue.

[rolandwalker]

@dekrueger Hi! Please PR if that's a partial fix. My assumption is that the tree-sitter port broke navigation, and that navigation could now be simplified.