preparing 2.4.18 updated and rebuilt the web site implement the new

* 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.
36 files changed