Merge branch 'mm/rebase-i-exec'

* mm/rebase-i-exec: git-rebase--interactive.sh: use printf instead of echo to print commit message git-rebase--interactive.sh: rework skip_unnecessary_picks test-lib: user-friendly alternatives to test [-d|-f|-e] rebase -i: add exec command to launch a shell command Conflicts: git-rebase--interactive.sh t/t3404-rebase-interactive.sh