[imp] [horde] large session entries in horde_sessionhandler

[liam hoekenga]

> What session *variable* contains these messages? This might help
> trapping down where it gets into the session data, if you are sure that
> message caching is turned off on your production server.

Er... there isn't a way to toggle message caching in the release 
version of IMP
4.0.3.  I've seen it's an option in HEAD, tho.

Does that mean that message caching is turned on by default in 4.0.x?

Liam