Added xmlRelaxNGSetParserStructuredErrors() to the API.

* relaxng.c include/libxml/relaxng.h: Added
  xmlRelaxNGSetParserStructuredErrors() to the API.
diff --git a/relaxng.c b/relaxng.c
index 7e92057..be962eb 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -7510,6 +7510,20 @@
     return (0);
 }
 
+void
+xmlRelaxNGSetParserStructuredErrors(
+				    xmlRelaxNGParserCtxtPtr ctxt,
+				    xmlStructuredErrorFunc serror,
+				    void *ctx)
+{
+    if (ctxt == NULL)
+        return;
+    ctxt->serror = serror;
+    ctxt->error = NULL;
+    ctxt->warning = NULL;
+    ctxt->userData = ctx;
+}
+
 #ifdef LIBXML_OUTPUT_ENABLED
 
 /************************************************************************