exim4 subscribes to changes in its .conf
exim local delivery works again

using transport = virtual_local_delivery which sends the stuff to
/var/maildir/username.  This could stand to be tidied up further
CRAM-MD5 auth with secrets in /etc/exim4/passwd
delete many crufts caused by cut&paste from dean

delivery to RT, shared mailboxes, ...
/etc/exim4/passwd no longer made by puppet