"rebase --onto A...B" replays history on the merge base between A and B

"rebase --onto A...B" replays history on the merge base between A and B

This is in spirit similar to "checkout A...B".  To re-queue a new set of
patches for a series that the original author prepared to apply on 'next'
on the same base as before, you would do something like this:

    $ git checkout next^0
    $ git am -s rerolled-series.mbox
    $ git rebase --onto next...jh/notes next

The first two commands recreates commits to be rebased as the original
author intended (i.e. applies directly on top of 'next'), and the rebase
command replays that history on top of the same commit the series being
replaced was built on (which is typically much older than the tip of
'next').

Signed-off-by: Junio C Hamano <gitster@pobox.com>