git config --global branch.autosetuprebase always
It's also good to set up git config --global git-up.rebase.arguments --preserve-merges. Please read my comment.
Thanks for advice @sheerun, but I think that provided scenarion:
You check out master branch
You do your feature on feature branch while origin/master also changes on remote side
You merge your feature branch to your local master, without calling git-up before
You run git-up what results in rebasing master on origin/master and you loose your merge history:
is just really bad habbit. You need to rebase your feature branch on top of origin/master first, and after that merge it in to the local master branch. It's just obvious for me.