fixed -- Channel._shutdown was being called twice when there were
consumers which resulted in the following error from RabbitMQ:
`{amqp_error,channel_error,"expected 'channel.open'",'channel.close'}`.
RabbitMQ would then close the connection.
fixed bug - connection.Connection.close wouldn't actually send
a close when there were channels with consumers due to a logic
error
Merge pull request #267 from atatsu/dbl_channel_close_fix

fixed channel.close and connection.close issues