Move verification of response packets up to a level where it makes sense.

Move verification of response packets up to a level where it makes sense.

Replace the user_dispatch_flag on connections with
conn_user_dispatch_p().

Remove the 'original' member from packet and instead have an upper
layer verify.

Rename packet valid_flag --> received_flag to reflect that we don't
verify.

Move _close_conn() --> conn_close().

Move packet flags into a single unsigned int, for portability.

(_read_packet): Don't verify packet.

(rs_conn_receive_packet): Don't touch PKT_OUT if there isn't a packet.

(rs_conn_receive_packet): Verify packet using packet_verify_response().