- Update courier-imap to 4.16.1
- Update maildrop to 2.8.2
- Update sqwebmail to 5.8.2
- Update courier-authlib to 0.66.2
- Some plist and Makefile modernization

Approved by:		oliver@ (as maintainer of various of these ports)
Differential Revision:	https://reviews.freebsd.org/D2391