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/timemodule.c b/Modules/timemodule.c
index d2817fb..c32b53d 100644
--- a/Modules/timemodule.c
+++ b/Modules/timemodule.c
@@ -509,7 +509,7 @@
         }
 
     /* Convert the unicode string to an ascii one */
-    fmt = PyUnicode_AsString(format);
+    fmt = _PyUnicode_AsString(format);
 
 	fmtlen = strlen(fmt);