Fix private name mangling. The symtable also must do mangles so that

the scope of names can be correctly determined.

Include/symtable.h

@@ -17,7 +17,7 @@ struct symtable {
         PyObject *st_stack;      /* stack of namespace info */
 	PyObject *st_global;     /* borrowed ref to MODULE in st_symbols */
 	int st_nblocks;          /* number of blocks */
-	char *st_private;        /* name of current class or NULL */
+	PyObject *st_private;        /* name of current class or NULL */
         int st_tmpname;          /* temporary name counter */
 	PyFutureFeatures *st_future; /* module's future features */
 };