libdparse fails parsing `alias foo = this`

[wilzbach]

Found in func.d at dmd.
Minimized:

class F {
    bool equals()
    {
        alias fd1 = this;
    }
}

It's because this as a type has been removed in #250. Specs say that

Type aliases can sometimes look indistinguishable from alias declarations:
The distinction is made in the semantic analysis pass.

So i suppose the commit should be reverted. The idea here is then that this will alias to the instance, always, and never to typeof(this)

No actually i see now that the PR was not merged.