This sort of comparison of complex numbers is not mathematically meaningful:

    i35 : 1+2*ii < 2. * ii

    o35 = false

    i36 : 1+2*ii ? 2. * ii

    o36 = >

    o36 : Keyword

See "compare(...)" in gmp.d and compare(left:Expr,right:Expr) in actors3.d.
Make it give an error message, as returning "incomparable" would allow z<w to
succeed with answer "false", deceiving the user.

Maybe the flagged ones should also return errors.
