Skip IPv6 for 'localhost' PYTHON-356

This works around Winsock's misfeature of re-trying connections 3 times before failing, making localhost connections slow on Windows. If you must use IPv6 on localhost pass ::1 as host.

Author: behackett

pymongo/pool.py

@@ -178,12 +178,15 @@ def create_connection(self, pair):
  This is a modified version of create_connection from
  CPython >=2.6.
  """
- # Don't try IPv6 if we don't support it.
+ host, port = pair or self.pair
+
+ # Don't try IPv6 if we don't support it. Also skip it if host
+ # is 'localhost' (::1 is fine). Avoids slow connect issues
+ # like PYTHON-356.
  family = socket.AF_INET
- if socket.has_ipv6:
+ if socket.has_ipv6 and host != 'localhost':
  family = socket.AF_UNSPEC
 
- host, port = pair or self.pair
  err = None
  for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
  af, socktype, proto, dummy, sa = res