* ws/rebase-p:
rebase: remove merges_option and a blank line
rebase: remove unused code paths from git_rebase__interactive__preserve_merges
rebase: remove unused code paths from git_rebase__interactive
rebase: add and use git_rebase__interactive__preserve_merges
rebase: extract functions out of git_rebase__interactive
rebase: reindent function git_rebase__interactive
rebase: update invocation of rebase dot-sourced scripts
rebase-interactive: simplify pick_on_preserving_merges