Import the new nrelease Makefile packaging and root template infrastructure

Import the new nrelease Makefile packaging and root template infrastructure
from the DragonFly Installer Team and make the following additional
augmentations:

* Use the default port package install location to retrieve packages.
* Pre-check that all required packages exist before doing anything
* Remove the root autologin (also means that gettytab and ~root/.login can
  be removed from the original template).
* Add an etc/issue file
* Add an 'installer' user (root uid)

Obtained-from: The DragonFly Installer Team:
    Chris Pressey, Devon O'Dell, Eirik Nygaard, Hiten Pandya & GeekGod