Keep mailbox indexes cached for a while after they've been closed. Should speed up at least multiple APPENDs.
Keep mailbox indexes cached for a while after they've been closed. Should
speed up at least multiple APPENDs.

--HG--
branch : HEAD

jkerihuel/dovecot,dscho/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,dscho/dovecot,dscho/dovecot,jkerihuel/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,dscho/dovecot,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot