Improve the error report on undefined REFs

Use the tree node to provide the error context instead
of the parser input which is not relevant anymore,
based on a suggestion by François Delyon <f.delyon@satimage.fr>

result/valid/xlink.xml.err

@@ -1,6 +1,4 @@
 ./test/valid/xlink.xml:450: element termdef: validity error : ID dt-arc already defined
 	<p><termdef id="dt-arc" term="Arc">An <term>arc</term> is contained within an e
 	                                  ^
-./test/valid/xlink.xml:530: element termref: validity error : IDREF attribute def references an unknown ID "dt-xlg"
-
-^
+./test/valid/xlink.xml:199: element termref: validity error : IDREF attribute def references an unknown ID "dt-xlg"

valid.c

@@ -6559,6 +6559,7 @@ xmlValidateCheckRefCallback(xmlListPtr ref_list, xmlValidCtxtPtr ctxt,
 int
 xmlValidateDocumentFinal(xmlValidCtxtPtr ctxt, xmlDocPtr doc) {
     xmlRefTablePtr table;
+    unsigned int save;
 
     if (ctxt == NULL)
         return(0);
@@ -6568,6 +6569,10 @@ xmlValidateDocumentFinal(xmlValidCtxtPtr ctxt, xmlDocPtr doc) {
 	return(0);
     }
 
+    /* trick to get correct line id report */
+    save = ctxt->finishDtd;
+    ctxt->finishDtd = 0;
+
     /*
      * Check all the NOTATION/NOTATIONS attributes
      */
@@ -6581,6 +6586,8 @@ xmlValidateDocumentFinal(xmlValidCtxtPtr ctxt, xmlDocPtr doc) {
     ctxt->doc = doc;
     ctxt->valid = 1;
     xmlHashScan(table, (xmlHashScanner) xmlValidateCheckRefCallback, ctxt);
+
+    ctxt->finishDtd = save;
     return(ctxt->valid);
 }