rust-chg: update name of the server process This is a copy of updateprocname() of hgclient.c. At this point, rust-chg is basically functional. I did dogfooding for a couple of weeks in 2018. There are a few remaining tasks: a. loop detection by CHGINTERNALMARK b. forward unsupported commands (notably serve -d) to real hg c. better handling of early server exception d. modernize codebase (2018 edition, impl trait, async/await) For (d), we'll probably want to switch to async-std, but I'm thinking of upgrading to Tokio 0.2 as an intermediate step since process API isn't ported to async-std yet. I'm pretty sure future migration to async-std will be painless compared to the mass rewrite from futures-0.1 to 0.3. https://github.com/async-rs/async-std/issues/22 Differential Revision: https://phab.mercurial-scm.org/D8383