phabricator: migrate [phabricator.auth] to [auth]
This resurrects the warning mechanism removed in
20a4543e9a2b. I'm not worried
about the copy/paste of the code for a brief transitional period.
dispatch: unify handling of None returned by a command function
A command function may return None in place of 0 just for convenience, but
dispatch() doesn't need to inherit that property. This patch makes it be
friendly to callers.
dispatch: minor code refactor
This hopefully makes things slightly easier to read.
Differential Revision: https://phab.mercurial-scm.org/D3537