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 complex3;

void main()
{
    cfloat c1 = 1f + 0i;
    cfloat c2 = 0f + 0i;
    c2 += 1f + 0i;
    assert(c1 == c2);
}