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/string.py b/Lib/string.py
index 03179fb..6117ac0 100644
--- a/Lib/string.py
+++ b/Lib/string.py
@@ -41,7 +41,7 @@
 
 
 # Construct a translation map for bytes.translate
-def maketrans(frm, to):
+def maketrans(frm: bytes, to: bytes) -> bytes:
     """maketrans(frm, to) -> bytes
 
     Return a translation table (a bytes object of length 256)
@@ -53,10 +53,10 @@
         raise ValueError("maketrans arguments must have same length")
     if not (isinstance(frm, bytes) and isinstance(to, bytes)):
         raise TypeError("maketrans arguments must be bytes objects")
-    L = bytes(range(256))
+    L = buffer(range(256))
     for i, c in enumerate(frm):
         L[c] = to[i]
-    return L
+    return bytes(L)
 
 
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