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/peephole.c b/Python/peephole.c
index 30789e4..b9b26fc 100644
--- a/Python/peephole.c
+++ b/Python/peephole.c
@@ -407,7 +407,7 @@
 			case LOAD_NAME:
 			case LOAD_GLOBAL:
 				j = GETARG(codestr, i);
-				name = PyUnicode_AsString(PyTuple_GET_ITEM(names, j));
+				name = _PyUnicode_AsString(PyTuple_GET_ITEM(names, j));
 				h = load_global(codestr, i, name, consts);
 				if (h < 0)
 					goto exitUnchanged;