Issue 8366 - Overriding const member function in conjunction with mutable overload causes a strange error

http://d.puremagic.com/issues/show_bug.cgi?id=8366

We MUST kill attribute inference with const. To implement it correctly without breaking overriding and overloading features, re-scanning and arrangement of vtbl entries is needed in the end of `ClassDeclaration::semantic`, it will decrease compile speed.

I think that is a big drawbacks than the benefit.