demo n3651 with macro's illustrating when "duplicate declaration" is needed (at least with clang3.5)

	//Purpose:
	// Test compiler implementation of
	// "variable templates" as described in:
	/*
	http://isocpp.org/files/papers/N3651.pdf
	*/
	// and as commented on here:
	/*
	http://en.cppreference.com/w/Talk:cpp/language/variable_template
	*/
	//Usage:
	// if defined(USE_DUP_DECL):
	// the "duplicate declaration"
	// (the term used at top of p. 3 of N3651)
	// outside the numeric_limits class template
	// is used.
	// else:
	// the "duplicate declaration"
	// outside the numeric_limits class template
	// is not used.
	//
	// if defined(USE_REF):
	// the reference of variable in the variable template
	// is taken
	// in the printT template function.
	// else:
	// the reference of variable in the variable template
	// is not taken
	// in the printT template function.
	//Result:
	// Using clang3.5 from:
	/*
	http://llvm.org/releases/3.5.0/clang+llvm-3.5.0-x86_64-linux-gnu-ubuntu-14.04.tar.xz
	*/
	// as it was on 2014-11-03:
	// if !defined(USE_REF):
	// compiles & runs OK (USE_DUP_DECL doesn't matter).
	// else if defined(USE_REF) && defined(USE_DUP_DECL):
	// compiles & runs OK
	// else (defined(USE_REF) && !defined(USE_DUP_DECL)):
	// fails link with error message:
	/*
	undefined reference to `numeric_limits<int>::min'
	*/
	//Conclusion:
	// when defined(USE_REF), must provide "duplicate declaration".
	//=======================================
	//#define USE_DUP_DECL
	template<typename T>
	struct numeric_limits
	{
	static const T min
	#if defined(USE_DUP_DECL)
	;
	#else
	={};
	#endif
	};
	#if defined(USE_DUP_DECL)
	//The following is the "duplicate declaration"
	//mentioned at the top of p. 3 of N3651.
	template<typename T>
	const T numeric_limits<T>::min = {};// definition of a static data member template
	#endif
	#include <iostream>
	template<typename T>
	void printT
	( T
	#define USE_REF
	#ifdef USE_REF
	const&
	#endif
	a_t
	)
	{
	std::cout<<a_t;
	}
	int main()
	{
	#if defined(USE_DUP_DECL)
	std::cout<<"defined(USE_DUPL_DECL)\n";
	#else
	std::cout<<"!defined(USE_DUPL_DECL)\n";
	#endif
	std::cout<<"numeric_limits<int>::min=";
	printT(numeric_limits<int>::min);
	std::cout<<"\n";
	return 0;
	}