rename: return error status if any rename/copy failed
Ever since
447ea621e50e (copy: propagate errors properly, 2007-12-06),
we have returned an error status if the source file did not
exist. That commit did not return error status for any other errors,
and it's unclear if that was on purpose or not. It seems to me like we
should return an error in the other cases to, so that's what this
patch does.
Differential Revision: https://phab.mercurial-scm.org/D4419