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