fixed xmlXIncludeParseFile to prevent overwriting XML_COMPLETE_ATTRS when

* xinclude.c: fixed xmlXIncludeParseFile to prevent
  overwriting XML_COMPLETE_ATTRS when setting pctxt->loadsubset
  (bug 166199)
* Makefile.am, python/tests/Makefile.am, xstc/Makefile.am: added
  code to add $(top_builddir)/.libs to LD_LIBRARY_PATH whenever
  PYTHONPATH is set, to assure new libxml2 routines are used.
diff --git a/xinclude.c b/xinclude.c
index 1e0a603..2e7d884 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -451,7 +451,7 @@
     if ((pctxt->directory == NULL) && (directory != NULL))
         pctxt->directory = (char *) xmlStrdup((xmlChar *) directory);
 
-    pctxt->loadsubset = XML_DETECT_IDS;
+    pctxt->loadsubset |= XML_DETECT_IDS;
 
     xmlParseDocument(pctxt);