revamped the elfgcchack.h format to cope with gcc4 change of aliasing

* doc/apibuild.py doc/elfgcchack.xsl: revamped the elfgcchack.h
  format to cope with gcc4 change of aliasing allowed scopes, had
  to add extra informations to doc/libxml2-api.xml to separate
  the header from the c module source.
* *.c: updated all c library files to add a #define bottom_xxx
  and reimport elfgcchack.h thereafter, and a bit of cleanups.
* doc//* testapi.c: regenerated when rebuilding the API
Daniel
diff --git a/xmlmodule.c b/xmlmodule.c
index b057371..8b0fab9 100644
--- a/xmlmodule.c
+++ b/xmlmodule.c
@@ -439,4 +439,6 @@
 
 #endif /* HAVE_OS2 */
 
+#define bottom_xmlmodule
+#include "elfgcchack.h"
 #endif /* LIBXML_MODULES_ENABLED */