streamclone: add support for cloning non append-only file The phaseroots are stored in a non append-only file in the repository. We include them in the stream too. Since they are not append-only, we have to keep a copy around while we hold the lock to be able to stream them later. Since phase get exchanged within the stream we can skip requesting them independently. As a side effect, this will fixes issue5648 once the feature is enabled by default.