- 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/string_s.cpp

@@ -18,11 +18,11 @@
 
 #include "precompiled.h"
 
+#include <string.h>
+
 #include "lib.h"
 #include "posix.h"	// SIZE_MAX
 
-#include <string.h>
-
 #ifndef PERFORM_SELF_TEST
 #define PERFORM_SELF_TEST 0
 #endif