Set returncode to subprocess2.TIMED_OUT instead of -9 when a process times out.

tests/subprocess2_test.py

Index: tests/subprocess2_test.py
diff --git a/tests/subprocess2_test.py b/tests/subprocess2_test.py
index dfc91f6078e225c348b032a4f7ef5a2f42eb62ca..448a82d343a4a8957037d8bea6834c744e311927 100755
--- a/tests/subprocess2_test.py
+++ b/tests/subprocess2_test.py
@@ -136,7 +136,7 @@ class Subprocess2Test(unittest.TestCase):
         self.exe + ['--sleep', '--stdout'],
         timeout=0.01,
         stdout=subprocess2.PIPE)
-    self.assertEquals(-9, returncode)
+    self.assertEquals(subprocess2.TIMED_OUT, returncode)
     self.assertEquals(['', None], out)
 
   def test_void(self):