UI improvements for "git history reword".
* ps/history-ergonomics-updates:
Documentation/git-history: document default for "--update-refs="
builtin/history: rename "--ref-action=" to "--update-refs="
builtin/history: replace "--ref-action=print" with "--dry-run"
builtin/history: check for merges before asking for user input
builtin/history: perform revwalk checks before asking for user input