[imp] remember expanded folders

[Chuck Hagenbuch]

Quoting Jan Schneider <jan@horde.org>:

> Uh, you're right. Shame on me. Almost. Not if the user logs out and in.
> How about that?

That'd require saving the folder tree in the prefs storage, and it can get 
pretty large. Also, you're in all kinds of trouble if the users uses another 
client to change their folders, then logs in to IMP again.

-chuck

--
Charles Hagenbuch, <chuck@horde.org>
"What was and what may be lie, like children whose faces we cannot see, in 
the arms of silence. All we ever have is here, now." - Ursula K. Le Guin