help topic: cosmetic improvements. First, use of :hg:`...` is replaced with ``hg ...``. The former syntax isn't useful outside core Mercurial. Second, a few instances of `...` are replaced with ``...``. The minirst parser doesn't distinguish between the two, but using docutils, the former results italics and the latter in fixed width text. Finally, a few extra ``...`` are added. With these changes, we could process the help topic with rst2html and put it somewhere appropriate on the internet.