Upgrade libxml2 to 2.7.3 to patch some vulnerabilities.
diff --git a/parserInternals.c b/parserInternals.c
index d7aa4cf..758c6b3 100644
--- a/parserInternals.c
+++ b/parserInternals.c
@@ -1399,7 +1399,8 @@
     if (input == NULL) {
 	return(NULL);
     }
-    input->filename = (char *) entity->URI;
+    if (entity->URI != NULL)
+	input->filename = (char *) xmlStrdup((xmlChar *) entity->URI);
     input->base = entity->content;
     input->cur = entity->content;
     input->length = entity->length;
@@ -1669,6 +1670,7 @@
     ctxt->depth = 0;
     ctxt->charset = XML_CHAR_ENCODING_UTF8;
     ctxt->catalogs = NULL;
+    ctxt->nbentities = 0;
     xmlInitNodeInfoSeq(&ctxt->node_seq);
     return(0);
 }