I am ready to take the blame for being the first to introduce
--detect-* options in diff-opts, with the directory-rename stuff.
However, since --find-copies-harder predates everything and is the
only one to be part of a release today, I'd think it would be much
more consistent to use --find- as a common prefix. And, last but not
least, shorter long options do not hurt.
At the same time, I noticed the manpage could benefit from a small
improvement.