Show usage string for 'git cherry -h'

Treat an "-h" option as a request for help, rather than an "Unknown commit -h" error. "cherry -h" could be asking to compare histories that leads to our HEAD and a commit that can be named as "-h". Strictly speaking, that may be a valid refname, but the user would have to say something like "tags/-h" to name such a pathological ref already, so it is not such a big deal. The "-h" option keeps its meaning even if preceded by other options or followed by other arguments. This keeps the command-line syntax closer to what parse_options would give and supports shell aliases like 'alias cherry="git cherry -v"' a little better. Signed-off-by: Jonathan Nieder <jrnieder@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>