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/_testcapimodule.c b/Modules/_testcapimodule.c
index 15bd899..4a00fb1 100644
--- a/Modules/_testcapimodule.c
+++ b/Modules/_testcapimodule.c
@@ -691,7 +691,7 @@
 }
 #endif
 
-/* Some tests of PyBytes_FromFormat().  This needs more tests. */
+/* Some tests of PyString_FromFormat().  This needs more tests. */
 static PyObject *
 test_string_from_format(PyObject *self, PyObject *args)
 {
@@ -699,10 +699,10 @@
 	char *msg;
 
 #define CHECK_1_FORMAT(FORMAT, TYPE) 			\
-	result = PyBytes_FromFormat(FORMAT, (TYPE)1);	\
+	result = PyString_FromFormat(FORMAT, (TYPE)1);	\
 	if (result == NULL)				\
 		return NULL;				\
-	if (strcmp(PyBytes_AsString(result), "1")) {	\
+	if (strcmp(PyString_AsString(result), "1")) {	\
 		msg = FORMAT " failed at 1";		\
 		goto Fail;				\
 	}						\