fixed warning non-virtual-dtor and minor code refactor (#1324)

fixed warning non-virtual-dtor and minor code refactor

Jamfile

@@ -247,10 +247,6 @@ rule warnings ( properties * )
 		result += <cflags>-Wno-c++11-long-long ;
 		result += <cflags>-Wno-variadic-macros ;
 
-# in C++98 mode there's no way to silence this warning
-# in the code (without final)
-		result += <cflags>-Wno-non-virtual-dtor ;
-
 # enable these warnings again, once the other ones are dealt with
 		result += <cflags>-Wno-weak-vtables ;
 		result += <cflags>-Wno-sign-compare ;

include/libtorrent/aux_/allocating_handler.hpp

@@ -62,10 +62,13 @@ namespace libtorrent { namespace aux
 		handler_storage(handler_storage const&);
 	};
 
-	struct error_handler_interface
+	struct TORRENT_EXTRA_EXPORT error_handler_interface
 	{
 		virtual void on_exception(std::exception const&) = 0;
 		virtual void on_error(error_code const&) = 0;
+
+	protected:
+		~error_handler_interface() {}
 	};
 
 	// this class is a wrapper for an asio handler object. Its main purpose

include/libtorrent/disk_io_job.hpp

@@ -44,7 +44,6 @@ POSSIBILITY OF SUCH DAMAGE.
 namespace libtorrent
 {
 	struct storage_interface;
-	using storage_interface = storage_interface;
 	struct cached_piece_entry;
 	class torrent_info;
 	struct add_torrent_params;
@@ -69,7 +68,6 @@ namespace libtorrent
 	// a lot of heap allocation churn of using general purpose
 	// containers.
 	struct TORRENT_EXTRA_EXPORT disk_io_job : tailqueue_node<disk_io_job>
-		, boost::noncopyable
 	{
 		disk_io_job();
 		~disk_io_job();

include/libtorrent/storage.hpp

@@ -565,6 +565,9 @@ namespace libtorrent
 	{
 		virtual int file_op(int const file_index, std::int64_t const file_offset
 			, span<file::iovec_t const> bufs, storage_error& ec) = 0;
+
+	protected:
+		~fileop() {}
 	};
 
 	// this function is responsible for turning read and write operations in the

src/storage.cpp

@@ -212,7 +212,7 @@ namespace libtorrent
 
 	} // anonymous namespace
 
-	struct write_fileop : fileop
+	struct write_fileop final : fileop
 	{
 		write_fileop(default_storage& st, int flags)
 			: m_storage(st)
@@ -300,7 +300,7 @@ namespace libtorrent
 		int m_flags;
 	};
 
-	struct read_fileop : fileop
+	struct read_fileop final : fileop
 	{
 		read_fileop(default_storage& st, int const flags)
 			: m_storage(st)