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/Include/object.h b/Include/object.h
index 061fe11..e96e6a7 100644
--- a/Include/object.h
+++ b/Include/object.h
@@ -431,10 +431,8 @@
 PyAPI_FUNC(void) _Py_BreakPoint(void);
 PyAPI_FUNC(void) _PyObject_Dump(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_Repr(PyObject *);
-PyAPI_FUNC(PyObject *) PyObject_ReprStr8(PyObject *);
-PyAPI_FUNC(PyObject *) _PyObject_Str(PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_Str(PyObject *);
-PyAPI_FUNC(PyObject *) PyObject_Unicode(PyObject *);
+#define PyObject_Unicode PyObject_Str /* Compatibility */
 PyAPI_FUNC(int) PyObject_Compare(PyObject *, PyObject *);
 PyAPI_FUNC(PyObject *) PyObject_RichCompare(PyObject *, PyObject *, int);
 PyAPI_FUNC(int) PyObject_RichCompareBool(PyObject *, PyObject *, int);
@@ -478,7 +476,7 @@
 PyAPI_FUNC(long) _Py_HashPointer(void*);
 
 /* Helper for passing objects to printf and the like */
-#define PyObject_REPR(obj) PyString_AS_STRING(PyObject_ReprStr8(obj))
+#define PyObject_REPR(obj) PyUnicode_AsString(PyObject_Repr(obj))
 
 /* Flag bits for printing: */
 #define Py_PRINT_RAW	1	/* No string quotes etc. */