Member expression qualifiers are wrong

[Rob Schluntz]

This compiles, but shouldn't:

struct S {
  int x;
};

int main() {
  const S s;
  s.x = 0;
}

s.x currently has type int, but should be const int.

[Rob Schluntz <rschlunt@…>]

In 487845d:

Add aggregate qualifiers to MemberExpr? type [fixes #65]