This files should be copied to /usr/src/release.

Options
- NOPORTS: Does not include a ports tree on the install media
- NOSRC: Does not include documentation

Targets:
- release: Sets up installation media for a prebuilt world and kernel
- packagesystem: Builds distributions and tars them
- system: Sets up a bootable system that runs the installer at boot
- cdrom: Makes an ISO image from the output of system

Missing features:
- Release documentation build
- Memstick images
- FTP area prep