Don't force booleans to return #t/#f in if

[khoborerkagoj]

From the tutorial exercise 1.4.3:
Consider the expression (if (fx> 3 4) (fxadd1 3) (fxlognot 5)):
fx> first compares it arguments, generates 0 or 1, and then returns #t or #f depending on the result.
if then evaluates the result, compares to #f, and then decides what to do.

The fix would be to have a different definition of emit-expr which would just generate 1 or 0 as the result of the boolean expression. This alternate form would be called only from the test expression of an if, so would not affect results. This would save us in the creation of the boolean.