make sure xmlCtxtReadFile and htmlCtxtReadFile go through the catalog

* HTMLparser.c parser.c: make sure xmlCtxtReadFile and htmlCtxtReadFile
  go through the catalog resolution.
* gentest.py testapi.c: fix a side effect wrning of the change
Daniel
diff --git a/HTMLparser.c b/HTMLparser.c
index 4f84d7c..b87b01f 100644
--- a/HTMLparser.c
+++ b/HTMLparser.c
@@ -6038,7 +6038,7 @@
 
     htmlCtxtReset(ctxt);
 
-    stream = xmlNewInputFromFile(ctxt, filename);
+    stream = xmlLoadExternalEntity(filename, NULL, ctxt);
     if (stream == NULL) {
         return (NULL);
     }