- config.h: massive improvements, much clearer.

- tentatively activate PCH if gcc > 3.4. remove XP_ defines (which were
undocumented; now in scripting/spidermonkey.h)
- rename some config defines
- move sysdep/debug.h to lib/debug.h (it's portable; was wrong all
along)
- grouped all debug heap related stuff to debug.h:debug_heap_*
- sysdep: fix circular include issue with debug.h

This was SVN commit r2427.

source/lib/lib.cpp

@@ -16,13 +16,13 @@
 
 #include "precompiled.h"
 
-#include "lib/types.h"
-#include "lib.h"
-
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
 
+#include "lib/types.h"
+#include "lib.h"
+
 #include "sysdep/sysdep.h"