rust-chg: have attach_io() simply take reference of AsRawFd object We no longer have to deal with the restriction of the Future type. Before, these file objects couldn't be references and that's the only reason why we had to make stderr an Option<T>. This fixes future type deduction issue of stderr = None, where rustc would complain that T of Option<T> couldn't be deduced. Differential Revision: https://phab.mercurial-scm.org/D8443

rust-chg: reimplement attach_io operation as async function In short, MessageLoop<Connection> was redesigned as Protocol<Connection>, and the protocol methods no longer consume self. API changes are briefly documented in the following page: https://docs.rs/tokio-hglib/0.3.0/tokio_hglib/struct.Protocol.html Differential Revision: https://phab.mercurial-scm.org/D8442

rust-chg: upgrade to futures-0.3 based libraries And do some trivial fixes: - BytesMut::put_u32_be() -> put_u32() - tokio_process -> tokio::process, CommandExt -> Command, spawn_async() -> spawn(), stdin() -> stdin - tokio_timer::sleep() -> tokio::time::delay_for() Differential Revision: https://phab.mercurial-scm.org/D8441