How to check at compile time if Default Constructor for a class exists?

[Bottled Gin via Digitalmars-d]

> It seems like saying that a constructor with all default 
> arguments is not a default constructor is a distinction without 
> meaning. What are you doing that you would care?
>

The Object.factory does not seem to consider a constructor with 
default arguments as a defaultConstructor. Consider the following 
code snippet. It works only when I uncomment line 3.

module foo;                               // 1
class Foo {				  // 2
   // this() {}				  // 3
   this(int n=0) {}		          // 4
}					  // 5
void main() {				  // 6
   auto obj = Object.factory("foo.Foo");	  // 7
   assert(obj !is null);			  // 8
   auto foo = cast(Foo) obj;		  // 9
   assert(foo !is null);			  // 10
}					  // 11