558452 fight with reg test and error report

* relaxng.c: tiny fix and provide more context on some errors
* result/relaxng/558452_0* test/relaxng/558452*: add some regression
  tests for the bugs
* Makefile.am runtest.c: fight with the fact streaming error messages
  can differ due to missing node context
diff --git a/relaxng.c b/relaxng.c
index a0ddcc6..6b83cfd 100644
--- a/relaxng.c
+++ b/relaxng.c
@@ -2374,6 +2374,9 @@
         } else {
             node = seq = NULL;
         }
+        if ((node == NULL) && (seq == NULL)) {
+            node = ctxt->pnode;
+        }
         xmlRelaxNGShowValidError(ctxt, err, node, seq, arg1, arg2);
     }
     /*
@@ -4682,6 +4685,7 @@
         return(-1);
     }
     xmlHashScan(grammar->refs, xmlRelaxNGParseImportRef, ctxt);
+    return(0);
 }
 
 /**