Normally the codereview plugin disables adding new commits
when not using the submit command. Unfortunately this makes
it impossible to use the Mercurial Queues extension at the
same time.

A feature called "Phases" was introduced in Mercurial 2.1
that allows marking commits as being secret; this means
they will never be pushed to the upstream repository.

We can take advantage of this feature to allow the use of
Mercurial Queues if the mq.secret option has been set in
hgrc(5) and a recent version of Mercurial is used.

R=golang-dev, rsc, minux.ma
CC=golang-dev
https://golang.org/cl/7398055