add a ref_count field. (soup_transfer_read, create_writer): Set initial

add a ref_count field. (soup_transfer_read, create_writer): Set initial

        * libsoup/soup-transfer.c (SoupReader, SoupWriter): add a
        ref_count field.
        (soup_transfer_read, create_writer): Set initial ref_count to 2
        (one for soup-transfer, one for the caller).
        (soup_transfer_read_ref, soup_transfer_read_unref): ref/unref a
        reader
        (soup_transfer_read_stop): Clears the GIOChannel callbacks and
        drops soup-transfer's ref.
        (soup_transfer_read_cancel): Now just a stop+unref
        (soup_transfer_write_ref, soup_transfer_write_unref,
        soup_transfer_write_stop, soup_transfer_write_cancel): Similarly.

        * libsoup/soup-message.c (soup_message_cleanup): when setting up
        the "finish reading" callbacks, unref the reader so it will be
        destroyed once it's done reading.
        (soup_message_requeue): Likewise.

        * libsoup/soup-queue.c (soup_queue_read_headers_cb): Update for
        prototype change (no longer returns a SoupTransferDone).
        (soup_queue_read_chunk_cb): Likewise.

        * libsoup/soup-server.c (read_headers_cb): Likewise