Merge branch 'jk/cherry-pick-0-mainline'

"git revert -m 0 $merge_commit" complained that reverting a merge needs to say relative to which parent the reversion needs to happen, as if "-m 0" weren't given. The correct diagnosis is that "-m 0" does not refer to the first parent ("-m 1" does). This has been fixed. * jk/cherry-pick-0-mainline: cherry-pick: detect bogus arguments to --mainline