Add 3-argument socket.create_connection() backport for Py2.6 (issue #162)

This function is also in ``future.backports.socket``, but that module
needs more testing. This function is simple enough to include separately
in ``future.backports.misc`` for now.

Author: edschofield

src/future/backports/http/client.py

@@ -75,7 +75,7 @@
 
 from future.backports.email import parser as email_parser
 from future.backports.email import message as email_message
-from future.backports.socket import create_connection as socket_create_connection
+from future.backports.misc import create_connection as socket_create_connection
 import io
 import os
 import socket

src/future/backports/misc.py

@@ -828,6 +828,52 @@ def clear(self):
         self.maps[0].clear()
 
 
+# Re-use the same sentinel as in the Python stdlib socket module:
+from socket import _GLOBAL_DEFAULT_TIMEOUT
+# Was: _GLOBAL_DEFAULT_TIMEOUT = object()
+
+
+def create_connection(address, timeout=_GLOBAL_DEFAULT_TIMEOUT,
+                      source_address=None):
+    """Backport of 3-argument create_connection() for Py2.6.
+
+    Connect to *address* and return the socket object.
+
+    Convenience function.  Connect to *address* (a 2-tuple ``(host,
+    port)``) and return the socket object.  Passing the optional
+    *timeout* parameter will set the timeout on the socket instance
+    before attempting to connect.  If no *timeout* is supplied, the
+    global default timeout setting returned by :func:`getdefaulttimeout`
+    is used.  If *source_address* is set it must be a tuple of (host, port)
+    for the socket to bind as a source address before making the connection.
+    An host of '' or port 0 tells the OS to use the default.
+    """
+
+    host, port = address
+    err = None
+    for res in getaddrinfo(host, port, 0, SOCK_STREAM):
+        af, socktype, proto, canonname, sa = res
+        sock = None
+        try:
+            sock = socket(af, socktype, proto)
+            if timeout is not _GLOBAL_DEFAULT_TIMEOUT:
+                sock.settimeout(timeout)
+            if source_address:
+                sock.bind(source_address)
+            sock.connect(sa)
+            return sock
+
+        except error as _:
+            err = _
+            if sock is not None:
+                sock.close()
+
+    if err is not None:
+        raise err
+    else:
+        raise error("getaddrinfo returns an empty list")
+
+
 # Back up our definitions above in case they're useful
 _OrderedDict = OrderedDict
 _Counter = Counter
@@ -837,13 +883,15 @@ def clear(self):
 __count_elements = _count_elements
 _recursive_repr = recursive_repr
 _ChainMap = ChainMap
+_create_connection = create_connection
 
 # Overwrite the definitions above with the usual ones
 # from the standard library:
 if sys.version_info >= (2, 7):
     from collections import OrderedDict, Counter
     from subprocess import check_output
     from itertools import count
+    from socket import create_connection
 
 if sys.version_info >= (3, 0):
     from math import ceil