Try to make sure TCP_NODELAY is set on INET sockets.

This is a nasty work around for: https://bugs.python.org/issue27456

It can't always be applied.  For example, it can't be applied to Linux
SSL sockets using the asyncio-provided loop.

src/ZEO/asyncio/base.py

@@ -1,11 +1,15 @@
 from struct import unpack
 import asyncio
 import logging
+import socket
+import sys
 
 from .marshal import encoder
 
 logger = logging.getLogger(__name__)
 
+INET_FAMILIES = socket.AF_INET, socket.AF_INET6
+
 class Protocol(asyncio.Protocol):
     """asyncio low-level ZEO base interface
     """
@@ -41,7 +45,16 @@ def close(self):
 
     def connection_made(self, transport):
         logger.info("Connected %s", self)
+
+        if (sys.version_info < (3, 6) and
+            hasattr(transport, '_sock') and
+            transport._sock.family in INET_FAMILIES
+            ):
+            # See https://bugs.python.org/issue27456 :(
+            transport._sock.setsockopt(
+                socket.IPPROTO_TCP, socket.TCP_NODELAY, True)
         self.transport = transport
+
         paused = self.paused
         output = self.output
         append = output.append