[PATCH] acl: add support for bookmarks [RFC]

[timeless]

Pierre-Yves David wrote:
> bundle2 and bundle1 will be totally opaque to user. We need to be more
> helpful here. Maybe mention Mercurial version number that will use the
> legacy protocol.

I don't think it's version level controlled. Since afaiu bitbucket was
using a new version of mercurial but w/ old repositories and I /think/
I was getting the bundle1 behavior. But perhaps I'm wrong.

It might be requirements controlled.
And it's probably possible to give the acl command a validator which
would be able to report which style it would use. But I'm not
volunteering to write that, and I'm definitely not claiming ownership
of the module.

I'm open to wording if someone can write it up. I'm not sure the
correct wording.