[CFT/RFC]: refactor bsd.prog.mk to understand multiple programs instead of a singular program

[Simon J. Gerraty]

>These discussions need backing up with a real roadmap, including detail on
>exactly what 8.3 and 7.4 users will have to do to ensure that the ports
>tree still works.

I've tested the ports tree converted to bmake - per the "patch" I
mentioned on a 7.1 box.  It worked for me.  Once the ports tree has
found or installed bmake, the system version makes no further
difference.

Obviously not a conclusive result, but yes this issue has been given
consideration.