Avoid hanging forever when the socket goes away and the only thing we're doing is writing.

If the connection closed during a flush_outbound with pending data, we
were in some cases (asyncore-based) looping forever. Checking each
time we enter the loop gets us a sensible exception in these cases.

pika/asyncore_adapter.py

@@ -54,6 +54,7 @@
 from heapq import heappush, heappop
 from errno import EAGAIN
 import pika.connection
+from pika.exceptions import *
 
 class RabbitDispatcher(asyncore.dispatcher):
     def __init__(self, connection):
@@ -108,6 +109,9 @@
 
     def flush_outbound(self):
         while self.outbound_buffer:
+            if self.connection_close:
+                # The connection was closed while we weren't looking!
+                raise ConnectionClosed(self.connection_close)
             self.drain_events()
 
     def drain_events(self):