Improve keeping both sides in sync during password authentication. #6493
Improve keeping both sides in sync during password authentication. #6493

If one side sends an ERROR message, ensure both sides will exchange the
same set of messages (with dummy values) before returning failure.
Allow one side to send an ABORT message, which will allow both sides to
end the protocol exchange early, returning failure. Sending of an ABORT
isn't done yet, as older clients won't react properly to receiving it.

An allocation or cedar error can leave the two sides out of sync, but
these probably mean the connection or the process itself is hosed.

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor