Issue #15989: Fix several occurrences of integer overflow
when result of PyInt_AsLong() or PyLong_AsLong() narrowed
to int without checks.

This is a backport of changesets 13e2e44db99d and 525407d89277.
diff --git a/Lib/test/test_poll.py b/Lib/test/test_poll.py
index d33af91..55294f8 100644
--- a/Lib/test/test_poll.py
+++ b/Lib/test/test_poll.py
@@ -1,6 +1,7 @@
 # Test case for the os.poll() function
 
 import os, select, random, unittest
+import _testcapi
 from test.test_support import TESTFN, run_unittest
 
 try:
@@ -150,6 +151,15 @@
         if x != 5:
             self.fail('Overflow must have occurred')
 
+        pollster = select.poll()
+        # Issue 15989
+        self.assertRaises(OverflowError, pollster.register, 0,
+                          _testcapi.SHRT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.register, 0,
+                          _testcapi.USHRT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.poll, _testcapi.INT_MAX + 1)
+        self.assertRaises(OverflowError, pollster.poll, _testcapi.UINT_MAX + 1)
+
 def test_main():
     run_unittest(PollTests)