rust-chg: reimplement run_command operation as async function The crafted state machine is no longer needed thanks to async/await. The state machine is basically rewritten as follows: - Ready(..) -> return .. - PollAgain(..) -> run .. and await - Err(..) -> return Err(..) Differential Revision: https://phab.mercurial-scm.org/D8445

--- a/rust/chg/src/lib.rs	Fri Apr 10 22:23:10 2020 +0900
+++ b/rust/chg/src/lib.rs	Fri Apr 10 22:44:51 2020 +0900
@@ -8,7 +8,7 @@
 //pub mod locator;
 pub mod message;
 pub mod procutil;
-//mod runcommand;
+mod runcommand;
 mod uihandler;
 
 //pub use clientext::ChgClientExt;