Merge branch 'js/builtin-add-i-cmds' into pu

"git add -i" that is getting rewritten in C has been extended to
cover subcommands other than the "patch".

* js/builtin-add-i-cmds:
  built-in add -i: offer the `quit` command
  built-in add -i: re-implement the `diff` command
  built-in add -i: implement the `patch` command
  built-in add -i: re-implement `add-untracked` in C
  built-in add -i: re-implement `revert` in C
  built-in add -i: implement the `update` command
  built-in add -i: prepare for multi-selection commands
  built-in add -i: allow filtering the modified files list