test_selectors: test_timeout fails sometimes on busy (slow) buildbots, relax

the unit test on max time (but be more strict on mon time). Example of failure:

http://buildbot.python.org/all/builders/x86%20OpenIndiana%203.x/builds/6978/steps/test/logs/stdio

======================================================================
FAIL: test_timeout (test.test_selectors.PollSelectorTestCase)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/export/home/buildbot/32bits/3.x.cea-indiana-x86/build/Lib/test/test_selectors.py", line 316, in test_timeout
    self.assertTrue(0.5 < t1 - t0 < 1.5, t1 - t0)
AssertionError: False is not true : 1.5033390671014786

Lib/test/test_selectors.py

@@ -313,7 +313,8 @@ class BaseSelectorTestCase(unittest.TestCase):
         t0 = time()
         self.assertFalse(s.select(1))
         t1 = time()
-        self.assertTrue(0.5 < t1 - t0 < 1.5, t1 - t0)
+        dt = t1 - t0
+        self.assertTrue(0.8 <= dt <= 1.6, dt)
 
     @unittest.skipUnless(hasattr(signal, "alarm"),
                          "signal.alarm() required for this test")