Parse tree conversion for "let fun f x = e in e end"
Correct a bug in grammar specification of = as a relational operator.
A bunch of overloads in test-script to make output more comprehensible.

Also include a new "big" test-case for letrec:

let fun f1 x = x * f2 (x - 1)
    and f2 y = if y = 2 then 1 else f1 (y + 2)
in
    f1 (3 + y)
end