dropped some iostream dependencies

include/libtorrent/lazy_entry.hpp

@@ -35,12 +35,15 @@ POSSIBILITY OF SUCH DAMAGE.
 
 #include <utility>
 #include <vector>
-#include <iosfwd>
 #include <string>
 #include "libtorrent/config.hpp"
 #include "libtorrent/assert.hpp"
 #include "libtorrent/size_type.hpp"
 
+#if TORRENT_USE_IOSTREAM
+#include <iosfwd>
+#endif
+
 namespace libtorrent
 {
 	struct lazy_entry;
@@ -227,7 +230,9 @@ namespace libtorrent
 		char const* m_end;
 	};
 
+#if TORRENT_USE_IOSTREAM
 	TORRENT_EXPORT std::ostream& operator<<(std::ostream& os, lazy_entry const& e);
+#endif
 
 }