Remove some redundancy from the DValue hierarchy: all subclasses had a 'type' field and identical implementations of virtual function getType(). Move these to DValue itself, and make getType() non-virtual.

module complex4;

void main()
{
    cfloat c = 2f + 3fi;
    float r = cast(float)c;
    ifloat i = cast(ifloat)c;
}