temp fixes, as long as we didn't adapt our mailbox tree code, cache the

temp fixes, as long as we didn't adapt our mailbox tree code, cache the
list.

Make use of the sorted list with id's from the session if the mailbox state
didn't change.

All performance related imap fixes were found after playing with thetereal.
If you want to try itt yourself:

tethereal -t a -ni lo -f 'port 143' -R 'imap.request'
with lo the interface.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@7476 7612ce4b-ef26-0410-bec9-ea0150e637f0