[PATCH 0 of 2] phase mouvement with rebase and graft (good ones)

[alain.leufroy at logilab.fr]

Ok, everything shall be ok this time. I hope you will be lenient as this is my first contribution
(or I can cut off a small finger as a punishment :-) )

Note that there is no change in the graft code as it actually does the trick. I've just added test
to validate the behaviour.

--

These 2 changesets fix phase mouvement with rebase and add test for graft.

Rebase:
  The idea is to _try_ to keep source phase on rebase.

Graft:
  The idea is not to keep the phase of the cherry-picked changesets
  because::

* draft is a copy if the "operations" made on the source changets while rebase is used to
  move changesets
* draft allow to reorder changesets

What do you think about the draft behaviour? It shall be same for transplant