Windows doesn't support negative timestamps. Skip the tests involving them

if os.name == "nt".

Lib/test/test_datetime.py

@@ -3,6 +3,7 @@
 See http://www.zope.org/Members/fdrake/DateTimeWiki/TestCases
 """
 
+import os
 import sys
 import pickle
 import cPickle
@@ -1426,11 +1427,17 @@ class TestDateTime(TestDate):
                               insane)
 
     def test_negative_float_fromtimestamp(self):
+        # Windows doesn't accept negative timestamps
+        if os.name == "nt":
+            return
         # The result is tz-dependent; at least test that this doesn't
         # fail (like it did before bug 1646728 was fixed).
         self.theclass.fromtimestamp(-1.05)
 
     def test_negative_float_utcfromtimestamp(self):
+        # Windows doesn't accept negative timestamps
+        if os.name == "nt":
+            return
         d = self.theclass.utcfromtimestamp(-1.05)
         self.assertEquals(d, self.theclass(1969, 12, 31, 23, 59, 58, 950000))