Merge branch 'rj/add-p-typo-reaction'

When the user responds to a prompt given by "git add -p" with an
unsupported command, list of available commands were given, which
was too much if the user knew what they wanted to type but merely
made a typo.  Now the user gets a much shorter error message.

* rj/add-p-typo-reaction:
  add-patch: response to unknown command
  add-patch: do not show UI messages on stderr

diff --cc add-patch.c
Simple merge

diff --cc t/t3701-add-interactive.sh
Simple merge