Merge branch 'en/rebase-incompatible-opts'
"git rebase" often ignored incompatible options instead of
complaining, which has been corrected.
* en/rebase-incompatible-opts:
rebase: provide better error message for apply options vs. merge config
rebase: put rebase_options initialization in single place
rebase: fix formatting of rebase --reapply-cherry-picks option in docs
rebase: clarify the OPT_CMDMODE incompatibilities
rebase: add coverage of other incompatible options
rebase: fix incompatiblity checks for --[no-]reapply-cherry-picks
rebase: fix docs about incompatibilities with --root
rebase: remove --allow-empty-message from incompatible opts
rebase: flag --apply and --merge as incompatible
rebase: mark --update-refs as requiring the merge backend