Catching IOError. Fixes #127

Under heavy load we get "No such file or directory"
error when updating callbacks.

I've failed to reproduce it with the tcpproxy setup,
so this bugfix is currently not covered with unittest.

momoko/connection.py

@@ -703,15 +703,21 @@ def _io_callback(self, future, result, fd=None, events=None):
             self.ioloop.remove_handler(self.fileno)
             future.set_exc_info(sys.exc_info())
         else:
-            if state == POLL_OK:
+            try:
+                if state == POLL_OK:
+                    self.ioloop.remove_handler(self.fileno)
+                    future.set_result(result)
+                elif state == POLL_READ:
+                    self.ioloop.update_handler(self.fileno, IOLoop.READ)
+                elif state == POLL_WRITE:
+                    self.ioloop.update_handler(self.fileno, IOLoop.WRITE)
+                else:
+                    future.set_exception(psycopg2.OperationalError("poll() returned %s" % state))
+            except IOError:
+                # Can happen when there are quite a lof of outstanding
+                # requests. See https://github.com/FSX/momoko/issues/127
                 self.ioloop.remove_handler(self.fileno)
-                future.set_result(result)
-            elif state == POLL_READ:
-                self.ioloop.update_handler(self.fileno, IOLoop.READ)
-            elif state == POLL_WRITE:
-                self.ioloop.update_handler(self.fileno, IOLoop.WRITE)
-            else:
-                future.set_exception(psycopg2.OperationalError("poll() returned %s" % state))
+                future.set_exception(psycopg2.OperationalError("IOError on socker"))
 
     def ping(self):
         """