select_select(): Closing bug #448351 the easy way, i.e. by changing

the "#ifdef MS_WINDOWS" to "#ifdef SELECT_USES_HEAP" and by
    setting SELECT_USES_HEAP when FD_SETSIZE > 1024.

    The indirection seems useful since this subtly changes the path
    that "normal" Windows programs take (where Timmie sez FD_SETSIZE =
    512).  If that's a problem for Windows, he has only one place to
    change.