fixing #130453 XInclude element with no href attribute fully integrating

* xinclude.c: fixing #130453 XInclude element with no href attribute
* relaxng.c rngparser.c include/libxml2/relaxng.h: fully integrating
  the compact syntax will require more work, postponed for the
  2.6.5 release.
Daniel
diff --git a/xinclude.c b/xinclude.c
index e4f9821..56f7350 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -1841,10 +1841,9 @@
      */
     href = xmlXIncludeGetProp(ctxt, cur, XINCLUDE_HREF);
     if (href == NULL) {
-        /* @@@@ */
-	xmlXIncludeErr(ctxt, ctxt->incTab[nr]->ref, 
-		       XML_XINCLUDE_NO_HREF, "no href\n", NULL);
-	return(-1);
+	href = xmlStrdup(BAD_CAST ""); /* @@@@ href is now optional */
+	if (href == NULL) 
+	    return(-1);
     }
     parse = xmlXIncludeGetProp(ctxt, cur, XINCLUDE_PARSE);
     if (parse != NULL) {