streamclone: tests phase exchange during stream clone We add a test dedicated to phases. As reported in issue 5648 stream from a non publishing server is currently broken (does not preserve the phase). We'll fix it with 'v2' support in the next changesets.

streamclone: add support for bundle2 based stream clone The feature put to use the various bits introduced previously. If the server supports it, the client will request its stream clone through bundle2 instead of the legacy 'stream_out' commands. The bundle2 version use the better 'v2' version of stream bundles. The 'v2' format is not finalized yet. Now that there are some code running it, we can start working on it again. Performance numbers are available at the end of this series.

pull: preindent some code Next changesets will add support for using stream cloning with bundle2. We introduce indentation change first for clarity.