problem with alias this and Tuple

[Johann Lermer]

Hi all,

I have a problem with Tuples and struct templates that contain an 
alias this:
```d
import std;

struct Element(T)
{
	T payload;
	alias payload this;

	this (T p)
	{
		payload = p;
	}
}

class Item {}

void main ()
{
	auto e = Element!Item (new Item());
	auto t = tuple(e);
}
```
dmd generates a warning: **Warning: struct Element has method 
toHash, however it cannot be called with const(Element!(Item)) 
this.
Element.toHash defined here: 
/usr/local/include/d/druntime/import/object.d(83)**

The culprit seems to be the 'alias payload this'. When I remove 
that line, the code works. However, in my code, I need that 
alias. Any ideas, what's wrong or what I could do? Thanks.