- Enable FLAVORS.
- Make make describe flavors aware.
- Add a qa check for unique package names amongst flavors.
- Make MOVEDlint understand flavors.
- Add a bit of sanity check to make sure FLAVORS stay lowercase.
- Various fixes.

Reviewed by:	portmgr
Sponsored by:	Absolight
Differential Revision:	https://reviews.freebsd.org/D12577