"server denied" instead of reconnecting

[Justin Sheehy <justin@linus.mitre.org>]

I am using nnimap 0.3.21 against a Cyrus 1.5.10 server.

After a period of inactivity, the server closes the connection with:

* BYE idle for too long

After that point, all attempts to use nnimap error with "server
denied".  nnimap does call nnimap-cb-bye at this point, but does not
later attempt to reopen the connection when the user does a 'g' or
'M-g' on an nnimap group, as it ought to.

I haven't poked around much in the code regarding this yet, so this is
just a bug report and not a fix.

-Justin