Experiment to speed up IMAP folder scannning

[Peter Bloomfield <PeterBloomfield MindSpring com>]

Problem:    incredibly long ping-time to IMAP server leads
             to slow Balsa startup, and often an instant ``normal 
exit''.

Fix:        experimental code for issuing multiple LIST/LSUB requests.

Patch:      see http://bugzilla.gnome.org/show_bug.cgi?id=61263

Disclaimer: *Seriously* experimental! It works with my
             Cyrus server, but I've no idea whether other servers, of
             any flavor, will cope with the overlapping requests. 
On the other hand...if you'd like to try it, I'd be most interested to 
read about your experience with it.

Thanks for all comments, suggestions, reactions, etc!

Peter