Rename PyUnicode_AsString -> _PyUnicode_AsString and
PyUnicode_AsStringAndSize -> _PyUnicode_AsStringAndSize to mark
them for interpreter internal use only.

We'll have to rework these APIs or create new ones for the
purpose of accessing the UTF-8 representation of Unicode objects
for 3.1.
diff --git a/Modules/grpmodule.c b/Modules/grpmodule.c
index 039f794..ca442e5 100644
--- a/Modules/grpmodule.c
+++ b/Modules/grpmodule.c
@@ -113,7 +113,7 @@
     py_str_name = PyObject_Str(pyo_name);
     if (!py_str_name)
 	    return NULL;
-    name = PyUnicode_AsString(py_str_name);
+    name = _PyUnicode_AsString(py_str_name);
     
     if ((p = getgrnam(name)) == NULL) {
 	PyErr_Format(PyExc_KeyError, "getgrnam(): name not found: %s", name);