The `i` keybinding in the files panel now accepts a range selection of
nodes: every selected file is unstaged, removed from the index if it
was tracked, and appended to `.gitignore` (or `.git/info/exclude` on
the other menu entry) on its own line.
Plumbing switched from a single node to a slice of nodes so the tracked
/untracked split unstage-and-rm each path before writing the list.
The single-file path keeps the existing `.gitignore`-self-ignore guard.
ffab5b6ac9