Patches from Michael Long

Patches from Michael Long
* implementing imap status cache in order to reduce
the amount of status calls generated from the newmail and filter plugin.
* enable the cumulative message account in left_main.php again

Patches reviewed by me. I fixed a few small things in newmail and I added RECENT status
calls in imap_mailbox.php in order to make the "only check recent mail"
option work.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@10697 7612ce4b-ef26-0410-bec9-ea0150e637f0