demandimport: pass proper level to __import__ in Python 3 demandimport was failing in Python 3 with a ValueError because __import__'s level=-1 has gone away (-1 means to try both relative and absolute imports and relative imports don't exist in Python 3). With this patch, demandimport still doesn't work in Python 3 (it fails when importing a non-package module).

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.

revsetbenchmark: add `::tip and draft()` to the canonical list The want to test element on different side of the iterators.

revset: cosmetic changes in spanset range comparison We use the python syntax for range comparison: `a < x < c`. This is shorter, more readable and less error prone. This comparison escaped the cleanup make in e2031c8ca4f8