Merge branch 'mh/verify-lock-error-report'

Bring consistency to error reporting mechanism used in "refs" API. * mh/verify-lock-error-report: ref_transaction_commit(): do not capitalize error messages verify_lock(): do not capitalize error messages verify_lock(): report errors via a strbuf verify_lock(): on errors, let the caller unlock the lock verify_lock(): return 0/-1 rather than struct ref_lock *