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/_gestalt.c b/Modules/_gestalt.c
index 3a7279f..462a6d2 100644
--- a/Modules/_gestalt.c
+++ b/Modules/_gestalt.c
@@ -38,7 +38,7 @@
 			"OSType arg must be string of 4 chars");
         return 0;
     }
-    memcpy((char *)&tmp, PyUnicode_AsString(v), 4);
+    memcpy((char *)&tmp, _PyUnicode_AsString(v), 4);
     *pr = (OSType)ntohl(tmp);
     return 1;
 }