Fixes Issue #14234: CVE-2012-0876: Randomize hashes of xml attributes

in the hash table internal to the pyexpat module's copy of the expat
library to avoid a denial of service due to hash collisions.
Patch by David Malcolm with some modifications by the expat project.

Modules/pyexpat.c

@@ -1156,6 +1156,8 @@ newxmlparseobject(char *encoding, char *namespace_separator, PyObject *intern)
     else {
         self->itself = XML_ParserCreate(encoding);
     }
+    XML_SetHashSalt(self->itself,
+                    (unsigned long)_Py_HashSecret.prefix);
     self->intern = intern;
     Py_XINCREF(self->intern);
     PyObject_GC_Track(self);