Fix assignment of move-and-copy emulated classes

[Flamefire]

This works on the bug described here: https://svn.boost.org/trac/boost/ticket/12194 and which was introduced here: https://github.com/boostorg/move/commit/4f9c2b62fbdcf5995ecf50a2ecf2494048a6696d#diff-6a11d48d06dd33c1193ffb3d794787fbR252

Testcode:

#include <boost/move/move.hpp>
#include <cassert>

class Foo{
    BOOST_COPYABLE_AND_MOVABLE(Foo)
public:
    int i;
    explicit Foo(int val): i(val){}
    Foo(BOOST_RV_REF(Foo) obj): i(obj.i) {}
    Foo& operator=(BOOST_RV_REF(Foo) rhs){ i = rhs.i; rhs.i = 0; return *this; }
    Foo& operator=(BOOST_COPY_ASSIGN_REF(Foo) rhs){ i = rhs.i; return *this; }
    template<class OTHER>
    Foo& operator=(const OTHER& rhs){ i = rhs.j; return *this; }
};

struct Bar{
    int j;
    explicit Bar(int val): j(val){}
};

int main(){
    Foo foo1(1);
    Foo foo2(2);
    Bar bar(3);
    assert(foo1.i == 1);
    assert(foo2.i == 2);
    assert(bar.j == 3);
    foo2 = foo1; // This works with this patch
    assert(foo1.i == 1);
    assert(foo2.i == 1);
    foo1 = bar;
    assert(foo1.i == 3);
    foo2 = boost::move(foo1);
    assert(foo1.i == 0);
    assert(foo2.i == 3);
    const Foo foo4(4);
    foo2 = foo4; // This fails in either
    assert(foo2.i == 4);
    assert(foo4.i == 4);
    return 0;
}

I get the feeling that BOOST_COPY_ASSIGN_REF(Foo) was a bad idea. Note that the above code works fine in C++11.

[igaztanaga]

Thanks for the patch.