preparing 2.4.18 updated and rebuilt the web site implement the new

* configure.in: preparing 2.4.18
* doc/*: updated and rebuilt the web site
* *.c libxml.h: implement the new IN_LIBXML scheme discussed with
  the Windows and Cygwin maintainers.
* parser.c: humm, changed the way the SAX parser work when
  xmlSubstituteEntitiesDefault(1) is set, it will then
  do the entity registration and loading by itself in case the
  user provided SAX getEntity() returns NULL.
* testSAX.c: added --noent to test the behaviour.
Daniel
diff --git a/xinclude.c b/xinclude.c
index dfd90ab..7fbcaca 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -14,6 +14,7 @@
  * TODO: add an node intermediate API and handle recursion at this level
  */
 
+#define IN_LIBXML
 #include "libxml.h"
 
 #include <string.h>