Commit 53d9b9b67 (Escaping tweak in git.kak, 2024-02-06) broke
blame-jump when the commit subject contains a single quote.
(Also on unbalanced "{" which is a rare edge case but we already have
it in our Git history.)
git.kak assumes that filenames don't contain ' or unbalanced {,
but we can't really make that assumption about people's names or
commit subjects.
Unfortunately the escaping here is very messy. We need to pass
arbitrary text to callbacks; maybe we should have closures that can
capture private temporary registers.
