Stacked branches status update

[Ian Clatworthy]

I spent most of last week merging bzr.dev into Robert's
stacked branches loom and reviewing each of the threads
in that loom. As Robert is very busy on related work, I
made the tweaks I wanted directly while reviewing. This
code is not yet merged to bzr.dev: my tweaks need to be
approved by Robert or someone else before that can happen.

This morning, I've updated my stacked branches loom with
the latest bzr.dev (rev 3489) and my tweaks. It's available
from http://people.ubuntu.com/~ianc/bzr/shallow-branch/ for
anyone who wants to test stacked branches. This is passing
the full test suite.

Today, I'm planning to make some tweaks based on Aaron's
feedback. See https://lists.ubuntu.com/archives/bazaar/2008q2/040079.html.
In particular:

1. The storage of the stacked-on branch will be moved from
   a custom file ('stacked-on') to an entry in branch.conf.

2. The terminology used in options and error messages will be
   changed from "shallow" to "stacked".

3. Anything else?

So there are 5 patches still to land into bzr.dev from Robert's
loom:

* one introduces a new repo format
* one introduces a new branch format
* 3 extend the UI.

The guts of the work are the first 2 of these. I'd like
Robert's advice on when the right time is to land these.
Should they come after his current work or before?

FWIW, the UI patches are largely independent of each other.
We could probably benefit from some further UI work (e.g.
adding an option to checkout like we've done for branch)
as well.

Ian C.