Deal with version-mismatch-header received from the server

Cope with unknown frame types better. Currently it gets horribly

confused about frame lengths.

Make client brutal by default, killing the program on any amqp

error. Only if the user disables this behaviour will the user get to

deal with error conditions themselves. Make use of amqp_rpc_reply

consistent (i.e. universal), and rename it something like amqp_errno.