When running git blame in a "git show" buffer, we annotate the youngest
version of the file that has the line referenced by the diff line
at cursor.
In case the cursor is on an added or context line, we simply show
the version from the surrounding commit.
When the cursor is on a deleted line, we show the parent commit,
which still has the deleted line. However there is a bug: we use
the line number in the new version of the file. Fix that.
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.
