Deprecation warning with boost 1.73.0 in copy.hpp

[rogerorr]

iostreams/copy.hpp includes <boost/bind.hpp> which causes a deprecation warning with boost 1.73.0 by simply #including this file.

..\boost\boost/bind.hpp(41): note: The practice of declaring the Bind placeholders (_1, _2, ...)
in the global namespace is deprecated. Please use <boost/bind/bind.hpp> + using
namespace boost::placeholders, or define BOOST_BIND_GLOBAL_PLACEHOLDERS to
retain the current behavior.

As far as I can see iostreams itself does not use the placeholders, so replacing the include with
#include <boost/bind/bind.hpp> will resolve the problem here; but of course with the risk of causing a downstream problem for anyone accidentally relying on _1 etc. at global scope.

[mclow]

Since Boost.iostreams did not use it, I removed the include in 87d113c.