"this" is treated as an lvalue.  For classes, it should
be an rvalue.  In particular, the following absurdity
compiles in v1.063 and v.2.047 but should not.

class Yikes
{
    int i;
    this() { this = null; }
}


void main()
{
    auto y = new Yikes();
}

See also discussion at
http://www.digitalmars.com/d/archives/digitalmars/D/this_as_lvalue_116836.html