This reverts r63675 based on the discussion in this thread:

 http://mail.python.org/pipermail/python-dev/2008-June/079988.html

Python 2.6 should stick with PyString_* in its codebase.  The PyBytes_* names
in the spirit of 3.0 are available via a #define only.  See the email thread.
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
index 35a3d27..f958145 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -495,7 +495,7 @@
     fnames = PyTuple_New(num_fields);
     if (!fnames) return NULL;
     for (i = 0; i < num_fields; i++) {
-        PyObject *field = PyBytes_FromString(fields[i]);
+        PyObject *field = PyString_FromString(fields[i]);
         if (!field) {
             Py_DECREF(fnames);
             return NULL;
@@ -514,7 +514,7 @@
     PyObject *s, *l = PyTuple_New(num_fields);
     if (!l) return 0;
     for(i = 0; i < num_fields; i++) {
-        s = PyBytes_FromString(attrs[i]);
+        s = PyString_FromString(attrs[i]);
         if (!s) {
             Py_DECREF(l);
             return 0;
@@ -588,7 +588,7 @@
         PyObject *s = PyObject_Repr(obj);
         if (s == NULL) return 1;
         PyErr_Format(PyExc_ValueError, "invalid integer value: %.400s",
-                     PyBytes_AS_STRING(s));
+                     PyString_AS_STRING(s));
         Py_DECREF(s);
         return 1;
     }
@@ -606,7 +606,7 @@
         PyObject *s = PyObject_Repr(obj);
         if (s == NULL) return 1;
         PyErr_Format(PyExc_ValueError, "invalid boolean value: %.400s",
-                     PyBytes_AS_STRING(s));
+                     PyString_AS_STRING(s));
         Py_DECREF(s);
         return 1;
     }
@@ -3286,7 +3286,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of mod, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of mod, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -4414,7 +4414,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of stmt, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of stmt, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5261,7 +5261,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of expr, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of expr, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5299,7 +5299,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of expr_context, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of expr_context, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5417,7 +5417,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of slice, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of slice, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5439,7 +5439,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of boolop, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of boolop, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5501,7 +5501,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of operator, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of operator, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5531,7 +5531,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of unaryop, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of unaryop, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5585,7 +5585,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of cmpop, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of cmpop, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;
@@ -5751,7 +5751,7 @@
 
         tmp = PyObject_Repr(obj);
         if (tmp == NULL) goto failed;
-        PyErr_Format(PyExc_TypeError, "expected some sort of excepthandler, but got %.400s", PyBytes_AS_STRING(tmp));
+        PyErr_Format(PyExc_TypeError, "expected some sort of excepthandler, but got %.400s", PyString_AS_STRING(tmp));
 failed:
         Py_XDECREF(tmp);
         return 1;