[MERGE] Stacked branches UI part 1 - push

[Martin Pool]

+        Option('reference',
+            help='Create a stacked branch that refers to another branch '
+                'for the commit history. Only the work not present in the '
+                'referenced branch is included in the branch created.',
+            type=unicode),
+        Option('stacked',
+            help='Create a stacked branch that references the public location '
+                'of the parent branch. See --reference for more information.'),
         ]

As I understand it these are the same except in one case the url is
explicitly given and in the other it is the public parent url.  Maybe the
names should be made more similar to show this, e.g.

  --reference-parent --reference=...
or
  --stacked --stack-url=...

and to make it clear that they're not two different things.

+ def _show_push_branch(br_from, revision_id, location, to_file, verbose=False,

This does more than just show it; I'd call it _push_branch.

I'm moving around the code to see what actually changed; more in a bit...

-- 
Martin