[svn r328] Fixed an issue with interfaces where the vtable type of a interface implemented could be invalid. Fixes several tango modules like, FileStream, ServerSocket and most tina cluster modules :)

module condexp1;

void main()
{
    char[] a = "hello";
    char[] b = "world";
    int i = 42;
    {
    char[] c = i > 50 ? b : a;
    assert(c is a);
    }
}