[tex4ht] curiosity about unicode.4hf

[Karl Berry]

    You can make a copy of unicode.4hf in your working dir and delete the
    line with ’. It will be converted as a character then.

Michal - the question is, should we do that in the sources? On the
theory that with -cunihtf -utf8, characters should be output, not
entities. It is not logical to output an entity for ' and not for `,
after all.

However, I have no particular clue how to affect the output only in the
case of those options, and I don't think we should change the default
output ... -k