help: suggest keyword search when no topic is found When `hg help foobar` fails, it now suggests using `hg help --keyword foobar` instead of printing a full page of basic commands. This should greatly increases discoverability of the `hg help --keyword` argument.

help: provide a more helpful message when no keyword are matched Before this changeset, when no topic were matching the provided keyword ( in command such as `hg help --keyword babar`) the output was empty. This is confusing and unhelpful for new users seeking assistance in the help. We now display: $ hg help --keyword babar abort: no matches (try "hg help" for a list of topics) This send users in a new direction where they may find what they are looking for.

revsetbenchmark: use optparse to retrieve argument We need more flexibility. For example we'll want to run the benchmark on other repository.

revsetbenchmark: add a usage message when no arguments are passed This increase the odd someone who didn't wrote will it find out how to use this script.