The new functions much better convey the intent behind the lock
request. This allows cleanly integrating noLock (for read) and dryRun
(write/exclusive) handling.
There are only minor changes to existing behavior with two exceptions:
- `tag` no longer accepts the `--no-lock` flag. As it replaces files in
the repository, this always requires an exclusive lock.
- `debug examine` now returns an error if both `--extract-pack` and
`--no-lock` are given.