[PATCH 0 of 1] [Preview] revset argument for rebase

[Pierre-Yves David]

Below is the first path for adding revset support in rebase. Two others will be
needed to handle corner case.

The target behaviour is as follow:

- rebase will move the strict content of the revset on the destination,
- if the revset contains ancestor of destination rebase will fail,
- if the revset have multiple root, all of root them should be moved,
- rebase won't strip descendant of revset element outside of the revset,
- rebase won't strip rebased changeset which have descendant outside of the
  revset.