Followup to r83869 and issue #8524: rename socket.forget() to socket.detach()

and make it return the file descriptor.

Lib/test/test_socket.py

@@ -655,17 +655,21 @@ class BasicTCPTest(SocketConnectedTest):
         self.serv_conn.send(MSG)
         self.serv_conn.shutdown(2)
 
-    def testForget(self):
-        # Testing forget()
-        f = self.cli_conn.fileno()
-        self.cli_conn.forget()
+    def testDetach(self):
+        # Testing detach()
+        fileno = self.cli_conn.fileno()
+        f = self.cli_conn.detach()
+        self.assertEqual(f, fileno)
+        # cli_conn cannot be used anymore...
         self.assertRaises(socket.error, self.cli_conn.recv, 1024)
         self.cli_conn.close()
+        # ...but we can create another socket using the (still open)
+        # file descriptor
         sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM, fileno=f)
         msg = sock.recv(1024)
         self.assertEqual(msg, MSG)
 
-    def _testForget(self):
+    def _testDetach(self):
         self.serv_conn.send(MSG)
 
 @unittest.skipUnless(thread, 'Threading required for this test.')