more fiddling with boolean expressions, etc.

more fiddling with boolean expressions, etc.

optimize away while(false), and transform while(true) ==> for(;;).

UNSAFE:

some expressions are optimized away when we're in boolean context and can
determine that the value will always be true or false.  For example:

    x() || true ==> always `true` in boolean context
    x() && false ==> always `false` in boolean context

It's not technically correct to drop these expressions since we drop the
function call too (that might have side effects); on the other hand, I can't
see any legitimate use for such expressions and they might simply indicate a
bug (we do warn about it).