[Evolution] Turn off header caching

[Murray Trainer <mtrainer central-data net>]

Hi,

Our evolution IMAP users login to diskless nodes with NFS home directories.  There is not much point in 
Evolution caching IMAP headers in this case as it has to write them back across the network via NFS as well 
as wasting disk space.  Is there a way to turn caching of IMAP headers off completely in Evolution?  Webmail 
clients such as Horde and Zimbra seem to manage this and the performance is OK.  Maybe it could be 
implemented the same as in Firefox where there is an option to use RAM instead of disk as the cache?

Thanks

Murray