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/xinclude.c b/xinclude.c
index 2e7d884..8801f1e 100644
--- a/xinclude.c
+++ b/xinclude.c
@@ -2468,3 +2468,5 @@
 
 #else /* !LIBXML_XINCLUDE_ENABLED */
 #endif
+#define bottom_xinclude
+#include "elfgcchack.h"