phabricator: add phabupdate command to update status in batch
Changing status (accept, etc) on the webpage is not very convenient -
currently there is no way to accept (or abandon etc.) a stack using a single
click or command.
This patch adds a `phabupdate` command that could be used to change status
in batch. It also supports `--comment` which will write a comment on the
last revision, which is similar to what we do using emails.
Differential Revision: https://phab.mercurial-scm.org/D127