Assert that given symbols name :PROGRAM mode functions.
(assert-program-mode my-fn your-fn)
(assert-program-mode fn1 fn2 ... fnk)
where each fni is a literal symbol which should have a program
mode definition. An error is raised if any fni is not a program mode
This is a pseudo-event, meaning it can be used in an event context but does
not (ever) change the world.