old scheme (False/None/0/'' == fail) made coding style
unnatural, did not allow use of mercurial commands as hooks.
new scheme (False/None/0 == pass) is pythonic, does not require peculiar
"return True" at ends of hooks, allows hooks like this:
[hooks]
# update working dir after push into this repo
changegroup.update = python:mercurial.commands.update
hook updates bugzilla bugs when it sees commit comments that mention
bug id, such as "i fixed bug 77".
only bugzilla 2.16 supported yet, but easy to extend. bugzilla versions
have different schema, i have not used later than 2.16.