The branch git+ssh://tunnel.chiark.greenend.org.uk//home/ianmdlvl/public-git/dgit.git wip.rebase.for-mcv.v1 now contains a prototype of this feature. NB, rebasing branch. Also, I haven't run the full dgit test suite on it even once so it may contain changes that break dgit proper.
I tested it ad-hoc with a rune like this: ~/things/Dgit/dgit/using-these git-debrebase downstream-rebase-launder-v0 HEAD~10 The command line API should be considered unstable. We'll probably give this thing a better name, in particular. Ian.
