rhg: add exit code to HgError::Abort() My previous attempts to have rhg end with correct exit code was more of bug hunting. I found cases which were failing and fixed them. But as one might expect, more tests started failing. Let's add exit code `HgError::Abort()` and make it users explicitly tell what exit code they want. Differential Revision: https://phab.mercurial-scm.org/D10838