Upstream in Launchpad adds confusion

[Martin Pool]

I do wonder if we want some combination of

 * retargeting existing mps to a different destination branch (or,
seamlessly creating a new mp)
 * within the mp ui, rebasing some revisions into a branch based off a
different destination (this would be a bit like the idea that lp
should be able to actually commit the merge, in that lp is actually
generating new commits)


-- 
Martin