addressing @minrk's PR feedback

* check tornado version
* log.warn about the monkeypatching

IPython/frontend/html/notebook/notebookapp.py

@@ -40,6 +40,7 b' from jinja2 import Environment, FileSystemLoader'
 from zmq.eventloop import ioloop
 ioloop.install()
 
+import tornado
 from tornado import httpserver
 from tornado import web
 
@@ -524,7 +525,7 b' class NotebookApp(BaseIPythonApplication):'
             except socket.error as e:
                 # XXX: remove the e.errno == -9 block when we require
                 # tornado >= 3.0
-                if e.errno == -9:
+                if e.errno == -9 and tornado.version_info[0] < 3:
                     # The flags passed to socket.getaddrinfo from
                     # tornado.netutils.bind_sockets can cause "gaierror:
                     # [Errno -9] Address family for hostname not supported"
@@ -533,7 +534,7 b' class NotebookApp(BaseIPythonApplication):'
                     # not cause this error, but the only way to do this is to
                     # monkeypatch socket to remove the AI_ADDRCONFIG attribute
                     saved_AI_ADDRCONFIG = socket.AI_ADDRCONFIG
-                    self.log.info('Monkeypatching socket to fix tornado bug')
+                    self.log.warn('Monkeypatching socket to fix tornado bug')
                     del(socket.AI_ADDRCONFIG)
                     try:
                         # retry the tornado call without AI_ADDRCONFIG flags