* cc/replace-edit:
Documentation: replace: describe new --edit option
replace: add --edit to usage string
replace: add tests for --edit
replace: die early if replace ref already exists
replace: refactor checking ref validity
replace: make sure --edit results in a different object
replace: add --edit option
replace: factor object resolution out of replace_object
replace: use OPT_CMDMODE to handle modes
replace: refactor command-mode determination