Merge branch 'en/rebase-merge-on-sequencer'

"git rebase --merge" as been reimplemented by reusing the internal machinery used for "git rebase -i". * en/rebase-merge-on-sequencer: rebase: implement --merge via the interactive machinery rebase: define linearization ordering and enforce it git-legacy-rebase: simplify unnecessary triply-nested if git-rebase, sequencer: extend --quiet option for the interactive machinery am, rebase--merge: do not overlook --skip'ed commits with post-rewrite t5407: add a test demonstrating how interactive handles --skip differently rebase: fix incompatible options error message rebase: make builtin and legacy script error messages the same