Fix two test cases in test_os. ftruncate raises IOError unlike all the others…

Fix two test cases in test_os.  ftruncate raises IOError unlike all the others which raise OSError.  And close() on some platforms doesn't complain when given an invalid file descriptor.

Lib/test/test_os.py

@@ -534,8 +534,10 @@ class Win32ErrorTests(unittest.TestCase):
         self.assertRaises(WindowsError, os.utime, test_support.TESTFN, 0)
 
 class TestInvalidFD(unittest.TestCase):
-    singles = ["fchdir", "fdopen", "close", "dup", "fdatasync", "fstat",
+    singles = ["fchdir", "fdopen", "dup", "fdatasync", "fstat",
                "fstatvfs", "fsync", "tcgetpgrp", "ttyname"]
+    #singles.append("close")
+    #We omit close because it doesn'r raise an exception on some platforms
     def get_single(f):
         def helper(self):
             if  getattr(os, f, None):
@@ -565,9 +567,10 @@ class TestInvalidFD(unittest.TestCase):
         if hasattr(os, "fpathconf"):
             self.assertRaises(OSError, os.fpathconf, 10, "PC_FILESIZEBITS")
 
+    #this is a weird one, it raises IOError unlike the others
     def test_ftruncate(self):
         if hasattr(os, "ftruncate"):
-            self.assertRaises(OSError, os.ftruncate, 10, 0)
+            self.assertRaises(IOError, os.ftruncate, 10, 0)
 
     def test_lseek(self):
         self.assertRaises(OSError, os.lseek, 10, 0, 0)