Michel Morin:  My previous fix for C++03 was incomplete. 
It does not consider user-defined conversions that convert an rvalue
into an lvalue and works incorrectly for types with such a conversion
operator.
For example, 

    struct foo
    {
        operator int&();
    };

 returns false_type. 
Attached a patch that fixes this problem. 
http://llvm.org/bugs/show_bug.cgi?id=13601

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@162644 91177308-0d34-0410-b5e6-96231b3b80d8