Bug fix: (flo:min x y) and (flo:max x y) now conform to IEEE 754-2008,
as minNum/maxNum.

When one input is a quiet NaN, they return the other input.  Only when
both inputs are NaN or one input is a signalling NaN do they return a
NaN, and in either case, it is a quiet NaN[*].  These trap only when
the floating-point invalid-operation exception is trapped.

[*] Caveat: The IEEE 754 committee is considering changing the
behaviour of these operations on signalling NaN, because the current
semantics is nonassociative: min(1, min(2, sNaN)) = 1, whereas
min(min(1, 2), sNaN) = qNaN.  So don't go around relying on this
semantics for sNaN inputs too heavily!
