Mercurial: Implementation of a rebasing feature – Tortarolo Stefano

Abstract
I'm going to introduce a feature that allows to move sequence of revisions from
one parent revision to another, a so called 'rebasing feature'. 

Rebasing can be useful in various situations: for instance, a user, who is 
developing on a local branch, would like to keep his patches up-to-date with
mainline stream. In this case it would be useful if he could be able to move
his commits on top of the mainline stream's one.

The implementation will have to take in consideration several aspects, some of
them Mercurial related, other regarding Rebasing in general. 

Mercurial, that is based on the idea of immutable history, doesn't allow
revisions to be moved easily, so the simplest rebasing process could be
somewhere tricky. It could require to have transient/inconsistent states that
will be removed at the end of the process.

More in general, a rebasing process could face some issues due to user
interruption and/or file conflicts. In the latter case the process will stop
and wait for user intervention, so it will be necessary to provide a way to
resume an interrupted process; in event of interruption/abortion the repository
must be left in a consistent state.
Moreover, a rebasing process should check if there are redundant commits (read
as 'already applied patches').