Assigning result of object-initialization to field on dynamic parameter

As per #305:
````
using System; 
class C {
   public int P1;
   public void M(dynamic d) {
       d.p = new C { P1 = 123 };
   }
}
````
The method body of M compiles to
````
var $tmp2 = $d.p;
var $tmp1 = new {sm_C}();
$tmp1.$P1 = 123;
$tmp2 = $tmp1;
````
This results in d.p never being assigned.