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/Modules/_sre.c b/Modules/_sre.c
index 342f9a0..808fb57 100644
--- a/Modules/_sre.c
+++ b/Modules/_sre.c
@@ -1715,7 +1715,7 @@
     size = PyObject_Length(string);
 #endif
 
-    if (PyBytes_Check(string) || bytes == size)
+    if (PyString_Check(string) || bytes == size)
         charsize = 1;
 #if defined(HAVE_UNICODE)
     else if (bytes == (Py_ssize_t) (size * sizeof(Py_UNICODE)))
@@ -1949,7 +1949,7 @@
 
     if (!args)
         return NULL;
-    name = PyBytes_FromString(module);
+    name = PyString_FromString(module);
     if (!name)
         return NULL;
     mod = PyImport_Import(name);
@@ -3416,7 +3416,7 @@
         Py_DECREF(x);
     }
 
-    x = PyBytes_FromString(copyright);
+    x = PyString_FromString(copyright);
     if (x) {
         PyDict_SetItemString(d, "copyright", x);
         Py_DECREF(x);