Merging the py3k-pep3137 branch back into the py3k branch.
No detailed change log; just check out the change log for the py3k-pep3137
branch.  The most obvious changes:

  - str8 renamed to bytes (PyString at the C level);
  - bytes renamed to buffer (PyBytes at the C level);
  - PyString and PyUnicode are no longer compatible.

I.e. we now have an immutable bytes type and a mutable bytes type.

The behavior of PyString was modified quite a bit, to make it more
bytes-like.  Some changes are still on the to-do list.
diff --git a/Lib/test/test_posix.py b/Lib/test/test_posix.py
index 3569453..efd5fb0 100644
--- a/Lib/test/test_posix.py
+++ b/Lib/test/test_posix.py
@@ -193,6 +193,11 @@
             if hasattr(st, 'st_flags'):
                 posix.lchflags(test_support.TESTFN, st.st_flags)
 
+    def test_environ(self):
+        for k, v in posix.environ.items():
+            self.assertEqual(type(k), str)
+            self.assertEqual(type(v), str)
+
 def test_main():
     test_support.run_unittest(PosixTester)