make sure we report errors if xmlNewInputFromFile() fails. avoid using

* libxml.h parserInternals.c xmlIO.c: make sure we report errors
  if xmlNewInputFromFile() fails.
* xmlreader.c: avoid using _private for the node or document
  elements.
Daniel
diff --git a/parserInternals.c b/parserInternals.c
index 6b3df55..7d18788 100644
--- a/parserInternals.c
+++ b/parserInternals.c
@@ -1445,8 +1445,11 @@
 		"new input from file: %s\n", filename);
     if (ctxt == NULL) return(NULL);
     buf = xmlParserInputBufferCreateFilename(filename, XML_CHAR_ENCODING_NONE);
-    if (buf == NULL)
+    if (buf == NULL) {
+        __xmlLoaderErr(ctxt, "failed to load external entity \"%s\"\n",
+                     (const char *) filename);
 	return(NULL);
+    }
 
     inputStream = xmlNewInputStream(ctxt);
     if (inputStream == NULL) {