Merge branch 'fc/transport-helper-sync-error-fix'

Make sure the marks are not written out when the transport helper did not finish happily, to avoid leaving a marks file that is out of sync with the reality. * fc/transport-helper-sync-error-fix: t5801 (remote-helpers): cleanup environment sets transport-helper: fix sync issue on crashes transport-helper: trivial cleanup transport-helper: propagate recvline() error pushing remote-helpers: make recvline return an error transport-helper: remove barely used xchgline()