So, now opEquals can be any of these:

```D
bool opEquals(S s);
bool opEquals(ref S s);
bool opEquals(const S s);
bool opEquals(const ref S s);

bool opEquals(S s) const;
bool opEquals(ref S s) const;
bool opEquals(const S s) const;
bool opEquals(const ref S s) const;
```

I'll update the spec after confirmation.