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_codecs.py b/Lib/test/test_codecs.py
index 22db2ca..5833c6d 100644
--- a/Lib/test/test_codecs.py
+++ b/Lib/test/test_codecs.py
@@ -802,7 +802,7 @@
         if sys.maxunicode > 0xffff:
             codecs.register_error("UnicodeInternalTest", codecs.ignore_errors)
             decoder = codecs.getdecoder("unicode_internal")
-            ab = "ab".encode("unicode_internal")
+            ab = "ab".encode("unicode_internal").decode()
             ignored = decoder(bytes("%s\x22\x22\x22\x22%s" % (ab[:4], ab[4:]),
                                     "ascii"),
                               "UnicodeInternalTest")
@@ -1265,7 +1265,9 @@
                 encodedresult = b""
                 for c in s:
                     writer.write(c)
-                    encodedresult += q.read()
+                    chunk = q.read()
+                    self.assert_(type(chunk) is bytes, type(chunk))
+                    encodedresult += chunk
                 q = Queue(b"")
                 reader = codecs.getreader(encoding)(q)
                 decodedresult = ""