fix pyflakes warning in test__select.py on PY3

Thanks to @fantix for original patch.

greentest/test__select.py

+import six
 import sys
 import os
 from gevent import select, socket
@@ -29,14 +30,11 @@ class TestSelectTypes(greentest.TestCase):
         sock = socket.socket()
         select.select([int(sock.fileno())], [], [], 0.001)
 
-    try:
-        long
-    except NameError:
-        pass
-    else:
+    if hasattr(six.builtins, 'long'):
         def test_long(self):
             sock = socket.socket()
-            select.select([long(sock.fileno())], [], [], 0.001)
+            select.select(
+                [six.builtins.long(sock.fileno())], [], [], 0.001)
 
     def test_string(self):
         self.switch_expected = False