def storbinary(cmd, file, blocksize, rest_offset = nil) # :yield: data
      if rest_offset
        file.seek(rest_offset, IO::SEEK_SET)
      end
      synchronize do
        with_binary(true) do
          conn = transfercmd(cmd)
          loop do
            buf = file.read(blocksize)
            break if buf == nil
            conn.write(buf)
            yield(buf) if block_given?
          end
          conn.close
          voidresp
        end
      end
    rescue Errno::EPIPE
      # EPIPE, in this case, means that the data connection was unexpectedly
      # terminated.  Rather than just raising EPIPE to the caller, check the
      # response on the control connection.  If getresp doesn't raise a more
      # appropriate exception, re-raise the original exception.
      getresp
      raise
    end
Puts the connection into binary (image) mode, issues the given server-side
command (such as "STOR myfile"), and sends the contents of the file named
+file+ to the server. If the optional block is given, it also passes it
the data, in chunks of +blocksize+ characters.