Fixed weird struct problem from downs, see mini/compile_structs1.d Rewrote DtoIndexStruct/Class , the old implementation were way too complex for what we really need now - since the DotVar changes.

struct Foo { int a, b, c; union Data { } Data data; }
struct Bar { int a, b; }
struct Baz { int a; union { Foo foo; Bar bar; } }
void test() { Baz baz; if (baz.bar.a) return; }