during an update, pull from master branch and reparent feature branch

[joachim-n]

Rather than do a git rebase, which could cause conflicts and require manual handling, we should instead reparent commits -- see http://blog.plover.com/prog/git-reorder.html for details.

[joachim-n]

Probably not going to implement this, as it would need to be able to handle rebase conflicts, and therefore the script would effectively end up driving git's conflict system, which is far more complexity than I want to get into.