This program is to decide if it should run
etc/interactive programs or etc/command programs.

It should live in etc/front.end and be linked to
names in bin that have programs/shell scripts in
etc/interactive and etc/command of the same name:

ln etc/front.end bin/window
for etc/command/window and etc/interactive/window

When user runs window, this executes etc/front.end
but argv[0] will have the name "window", which
front.end will use to build the two program names
etc/interactive/window and etc/command/window.
