clone: only use stream when we understand the revlog format This patch fixes issues with stream cloning in the presense of parentdelta, lwcopy and similar additions that change the interpretation of the revlog format, or the format itself. Currently, the stream capability is sent like this: stream=<version of changelog> But the client doesn't actually check the version number; also, it only checks the changelog and it doesn't capture the interpretation-changes and flag-changes in parentdelta and lwcopy. This patch removes the 'stream' capability whenever we use a non-basic revlog format, to prevent old clients from receiving incorrect data. In those cases, a new capability called 'streamreqs' is added instead. Instead of a revlog version, it comes with a list of revlog-format relevant requirements, which are a subset of the repository requirements, excluding things that are not relevant for stream. New clients use this to determine whether or not they can stream. Old clients only look for the 'stream' capability, as always. New servers will still send this when serving old repositories.