cleanup handlers run in the order in which they are added. As Go calls
init() functions in lexical order, the cleanup handler from global.go
was registered before that from lock.go, which is the correct order.
Make this order explicit to ensure that this won't break accidentally.
Now that lockRepo receives a context, it is possible that it is canceled
before a lock was created. Thus `unlockRepo` must be able to handle this
case.
cmd/restic/globals.go already provides Printf, Println and Warnf wrapper
which get their output streams from the globalOptions object. This
allows for stream replacements when testing.
errors.Fatalf wraps a error and just keeps an error message as a string.
This prevents the `restic.IsAlreadyLocked(err)` check from working as
the error is no longer an ErrAlreadyLocked.
Just add an additional remark to the error using `errors.WithMessage`.
