make skip IncompatibleProtocolError as optional for client to adapt scenarios like ELB connection

In my scenario with configurations
* tornado server publishes message to MQ through ELB
* ELB in front of rabbitMQ(s)
* rabbitMQ setup as a cluster

when some of rabbitMQ is down and the cluster is not in function, tornado's pika connection with receive error like


"""
[2014-11-19 01:04:30,841][ERROR  ][tornado.application:681] : Exception in I/O handler for fd 21#012Traceback (most recent call last):#01
2  File "/tornado/ioloop.py", line 671, in start#012    self._handlers[fd](fd,
events)#012  File "/tornado/stack_context.py", line 331, in wrapped#012    raise_exc_info(exc)#012  File "/tornado/stack_context.py", line 302, in wrapped#012
    ret = fn(*args, **kwargs)#012  File "/pika/adapters/base_connection.py”, line 322, in _handle_events#012    self._handle_read()#012 
File "/pika/adapters/base_connection.py", line 348, in _handle_read#012   
return self._handle_disconnect()#012  File "/pika/adapters/base_connection.py", line 248, in _handle_disconnect#012    self._adapter_disconnect()#012  File "/pika/adapters/tornado_connection.py", line 75, in _adapter_disconnect#012   
super(TornadoConnection, self)._adapter_disconnect()#012  File "/pika/adapters/base_connection.py", line 137, in _adapter_disconnect#012
self._check_state_on_disconnect()#012  File "/pika/adapters/base_connection.py", line 149, in _check_state_on_disconnect#012   
raise exceptions.IncompatibleProtocolError#012IncompatibleProtocolError
"""

And all the error handling and re-connection mechanism will NOT be invoked since the exception breaks the calls to _on_connection_closed which registered error handling callbacks.
```
    def _handle_disconnect(self):
        """Called internally when the socket is disconnected already
        """
        self._adapter_disconnect()   # BREAKS HERE !
        self._on_connection_closed(None, True)
```

In this scenario "IncompatibleProtocolError" is not treated as severe error and the connection can be recovered by re-connecting. Therefore I proposed that client can have option to skip this error for the appropriate scenario.

Thanks.