Deprecated boost::core::is_same and the associated header.

Moved is_same implementation to detail (both directory and namespace)
to use in the public headers and avoid introducing new dependencies.
The documentation now recommends users to use Boost.TypeTraits or
C++ standard library instead.

Also, removed unnecessary includes and added missing ones in a few
places.

test/quick.cpp

@@ -16,13 +16,12 @@
 #include <boost/core/explicit_operator_bool.hpp>
 #include <boost/get_pointer.hpp>
 #include <boost/core/ignore_unused.hpp>
-#include <boost/core/is_same.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <boost/noncopyable.hpp>
 #include <boost/core/null_deleter.hpp>
 #include <boost/core/fclose_deleter.hpp>
 #include <boost/core/pointer_traits.hpp>
-#include <boost/ref.hpp>
+#include <boost/core/ref.hpp>
 #include <boost/core/scoped_enum.hpp>
 #include <boost/core/typeinfo.hpp>
 #include <boost/core/underlying_type.hpp>