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/cgensupport.c b/Modules/cgensupport.c
index 965f7b4..7e7d0ff 100644
--- a/Modules/cgensupport.c
+++ b/Modules/cgensupport.c
@@ -119,10 +119,10 @@
 	PyObject *v;
 	if (!PyArg_GetObject(args, nargs, i, &v))
 		return 0;
-	if (!PyBytes_Check(v)) {
+	if (!PyString_Check(v)) {
 		return PyErr_BadArgument();
 	}
-	*p_arg = PyBytes_AsString(v);
+	*p_arg = PyString_AsString(v);
 	return 1;
 }