Fix leak of duplicate file descriptor for bound sockets.

`socket.fromfd` does not close the original file descriptor, so we have to explicitly close it to avoid a leak.

See also:
http://bugs.python.org/issue10099

gunicorn/sock.py

@@ -25,10 +25,13 @@ class BaseSocket(object):
         self.cfg_addr = address
         if fd is None:
             sock = socket.socket(self.FAMILY, socket.SOCK_STREAM)
+            bound = False
         else:
             sock = socket.fromfd(fd, self.FAMILY, socket.SOCK_STREAM)
+            os.close(fd)
+            bound = True
 
-        self.sock = self.set_options(sock, bound=(fd is not None))
+        self.sock = self.set_options(sock, bound=bound)
 
     def __str__(self, name):
         return "<socket %d>" % self.sock.fileno()

tests/test_sock.py

@@ -6,10 +6,13 @@ except ImportError:
 from gunicorn import sock
 
 
+@mock.patch('os.close')
 @mock.patch('os.getpid')
 @mock.patch('os.unlink')
 @mock.patch('socket.fromfd')
-def test_unix_socket_close_unlink(fromfd, unlink, getpid):
-    gsock = sock.UnixSocket('test.sock', mock.Mock(), mock.Mock(), mock.Mock())
+def test_unix_socket_close_unlink(fromfd, unlink, getpid, close):
+    fd = 42
+    gsock = sock.UnixSocket('test.sock', mock.Mock(), mock.Mock(), fd=fd)
     gsock.close()
     unlink.assert_called_with("test.sock")
+    close.assert_called_with(fd)