Add comment about dormant bug when sending a lot of data to a slow node

This mainly concerns the storage node, and depending on how its polling loop is
changed, the following crash could happen again during replication:

  File "neo/scripts/neostorage.py", line 66, in main
    app.run()
  File "neo/storage/app.py", line 147, in run
    self._run()
  File "neo/storage/app.py", line 178, in _run
    self.doOperation()
  File "neo/storage/app.py", line 258, in doOperation
    _poll(0)
  File "neo/lib/event.py", line 231, in _poll
    conn.writable()
  File "neo/lib/connection.py", line 418, in writable
    if self.connector.send():
  File "neo/lib/connector.py", line 179, in send
    n = self.socket.send(msg)
  File "ssl.py", line 719, in send
    v = self._sslobj.write(data)
OverflowError: string longer than 2147483647 byte

neo/lib/connector.py

@@ -174,7 +174,11 @@ class SocketConnector(object):
         self._error('recv')
 
     def send(self):
-        # XXX: unefficient for big packets
+        # XXX: Inefficient for big packets. In any case, we should make sure
+        #      that 'msg' does not exceed 2GB with SSL (OverflowError).
+        #      Before commit 1a064725b81a702a124d672dba2bcae498980c76,
+        #      this happened when many big AddObject packets were sent
+        #      for a single replication chunk.
         msg = ''.join(self.queued)
         if msg:
             try: