Major overhaul of timeout sockets:

- setblocking(0) and settimeout(0) are now equivalent, and ditto for
  setblocking(1) and settimeout(None).

- Don't raise an exception from internal_select(); let the final call
  report the error (this means you will get an EAGAIN error instead of
  an ETIMEDOUT error -- I don't care).

- Move the select to inside the Py_{BEGIN,END}_ALLOW_THREADS brackets,
  so other theads can run (this was a bug in the original code).

- Redid the retry logic in connect() and connect_ex() to avoid masking
  errors.  This probably doesn't work for Windows yet; I'll fix that
  next.  It may also fail on other platforms, depending on what
  retrying a connect does; I need help with this.

- Get rid of the retry logic in accept().  I don't think it was needed
  at all.  But I may be wrong.

Lib/test/test_timeout.py

@@ -59,17 +59,17 @@ class CreationTestCase(unittest.TestCase):
         self.assertRaises(ValueError, self.sock.settimeout, -1L)
         self.assertRaises(ValueError, self.sock.settimeout, -1.0)
 
-    def testTimeoutThenoBlocking(self):
+    def testTimeoutThenBlocking(self):
         "Test settimeout() followed by setblocking()"
         self.sock.settimeout(10)
         self.sock.setblocking(1)
         self.assertEqual(self.sock.gettimeout(), None)
         self.sock.setblocking(0)
-        self.assertEqual(self.sock.gettimeout(), None)
+        self.assertEqual(self.sock.gettimeout(), 0.0)
 
         self.sock.settimeout(10)
         self.sock.setblocking(0)
-        self.assertEqual(self.sock.gettimeout(), None)
+        self.assertEqual(self.sock.gettimeout(), 0.0)
         self.sock.setblocking(1)
         self.assertEqual(self.sock.gettimeout(), None)