We're now sniffing the incoming data to verify the server has sent a
full response, instead of passing partial data to our IMAP parser.
Our parser really can't handle partial input very well, so for the time
being, this heuristic does a much better job of verifying we have full
response before parsing.
It doesn't yet handle unprompted untagged reponses, nor the
"continuation request" responses that start with a `+`, but we don't
fully support those yet.
34adf9eeae