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/Python/compile.c b/Python/compile.c
index 942ca1f52..4600589 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -1300,7 +1300,7 @@
 				PyObject_REPR(name), 
 				PyBytes_AS_STRING(c->u->u_name), 
 				reftype, arg,
-				PyUnicode_AsString(co->co_name),
+				_PyUnicode_AsString(co->co_name),
 				PyObject_REPR(co->co_freevars));
 			Py_FatalError("compiler_make_closure()");
 		}