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/parsermodule.c b/Modules/parsermodule.c
index 4056816..2a61eec 100644
--- a/Modules/parsermodule.c
+++ b/Modules/parsermodule.c
@@ -718,7 +718,7 @@
                     Py_DECREF(o);
                 }
             }
-            temp_str = PyUnicode_AsStringAndSize(temp, &len);
+            temp_str = _PyUnicode_AsStringAndSize(temp, &len);
             strn = (char *)PyObject_MALLOC(len + 1);
             if (strn != NULL)
                 (void) memcpy(strn, temp_str, len + 1);
@@ -807,7 +807,7 @@
             if (res && encoding) {
                 Py_ssize_t len;
                 const char *temp;
-                temp = PyUnicode_AsStringAndSize(encoding, &len);
+                temp = _PyUnicode_AsStringAndSize(encoding, &len);
                 res->n_str = (char *)PyObject_MALLOC(len + 1);
                 if (res->n_str != NULL && temp != NULL)
                     (void) memcpy(res->n_str, temp, len + 1);