Merge branch 'dl/branch-from-3dot-merge-base'

"git branch new A...B" and "git checkout -b new A...B" have been taught that in their contexts, the notation A...B means "the merge base between these two commits", just like "git checkout A...B" detaches HEAD at that commit. * dl/branch-from-3dot-merge-base: branch: make create_branch accept a merge base rev t2018: cleanup in current test