Forward-port of r52136,52138: a review of overflow-detecting code.

* unified the way intobject, longobject and mystrtoul handle
  values around -sys.maxint-1.

* in general, trying to entierely avoid overflows in any computation
  involving signed ints or longs is extremely involved.  Fixed a few
  simple cases where a compiler might be too clever (but that's all
  guesswork).

* more overflow checks against bad data in marshal.c.

* 2.5 specific: fixed a number of places that were still confusing int
  and Py_ssize_t.  Some of them could potentially have caused
  "real-world" breakage.

* list.pop(x): fixing overflow issues on x was messy.  I just reverted
  to PyArg_ParseTuple("n"), which does the right thing.  (An obscure
  test was trying to give a Decimal to list.pop()... doesn't make
  sense any more IMHO)

* trying to write a few tests...
diff --git a/Lib/test/list_tests.py b/Lib/test/list_tests.py
index 14b54c7..7c6623a 100644
--- a/Lib/test/list_tests.py
+++ b/Lib/test/list_tests.py
@@ -269,7 +269,6 @@
         self.assertRaises(TypeError, a.insert)
 
     def test_pop(self):
-        from decimal import Decimal
         a = self.type2test([-1, 0, 1])
         a.pop()
         self.assertEqual(a, [-1, 0])
@@ -281,8 +280,6 @@
         self.assertRaises(IndexError, a.pop)
         self.assertRaises(TypeError, a.pop, 42, 42)
         a = self.type2test([0, 10, 20, 30, 40])
-        self.assertEqual(a.pop(Decimal(2)), 20)
-        self.assertRaises(IndexError, a.pop, Decimal(25))
 
     def test_remove(self):
         a = self.type2test([0, 0, 1])
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index f3bdbe2..f7cf811 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -156,6 +156,11 @@
         S = [10, 20, 30]
         self.assertEqual(any(x > 42 for x in S), False)
 
+    def test_neg(self):
+        x = -sys.maxint-1
+        self.assert_(isinstance(x, int))
+        self.assertEqual(-x, sys.maxint+1)
+
     def test_apply(self):
         def f0(*args):
             self.assertEqual(args, ())
@@ -702,9 +707,11 @@
                         pass
 
         s = repr(-1-sys.maxint)
-        self.assertEqual(int(s)+1, -sys.maxint)
+        x = int(s)
+        self.assertEqual(x+1, -sys.maxint)
+        self.assert_(isinstance(x, int))
         # should return long
-        int(s[1:])
+        self.assertEqual(int(s[1:]), sys.maxint+1)
 
         # should return long
         x = int(1e100)
diff --git a/Lib/test/test_long.py b/Lib/test/test_long.py
index 7b0c7b0..ae132ad 100644
--- a/Lib/test/test_long.py
+++ b/Lib/test/test_long.py
@@ -247,17 +247,23 @@
             "long(-sys.maxint-1) != -sys.maxint-1")
 
         # long -> int should not fail for hugepos_aslong or hugeneg_aslong
+        x = int(hugepos_aslong)
         try:
-            self.assertEqual(int(hugepos_aslong), hugepos,
+            self.assertEqual(x, hugepos,
                   "converting sys.maxint to long and back to int fails")
         except OverflowError:
             self.fail("int(long(sys.maxint)) overflowed!")
+        if not isinstance(x, int):
+            raise TestFailed("int(long(sys.maxint)) should have returned int")
+        x = int(hugeneg_aslong)
         try:
-            self.assertEqual(int(hugeneg_aslong), hugeneg,
+            self.assertEqual(x, hugeneg,
                   "converting -sys.maxint-1 to long and back to int fails")
         except OverflowError:
             self.fail("int(long(-sys.maxint-1)) overflowed!")
-
+        if not isinstance(x, int):
+            raise TestFailed("int(long(-sys.maxint-1)) should have "
+                             "returned int")
         # but long -> int should overflow for hugepos+1 and hugeneg-1
         x = hugepos_aslong + 1
         try:
@@ -282,6 +288,17 @@
         self.assert_(type(y) is long,
             "overflowing int conversion must return long not long subtype")
 
+        # long -> Py_ssize_t conversion
+        class X(object):
+            def __getslice__(self, i, j):
+                return i, j
+
+        self.assertEqual(X()[-5L:7L], (-5, 7))
+        # use the clamping effect to test the smallest and largest longs
+        # that fit a Py_ssize_t
+        slicemin, slicemax = X()[-2L**100:2L**100]
+        self.assertEqual(X()[slicemin:slicemax], (slicemin, slicemax))
+
 # ----------------------------------- tests of auto int->long conversion
 
     def test_auto_overflow(self):