ALL: Add code to help stop people from accidentally using "bad" APIs

A new header file common/forbidden.h is included by scummsys.h and it
re-#defines numerous symbols like fopen(), fread(), system(), etc. with
garbage, in order to provoke compile errors in any code using them.

If a .cpp file really *must* use any of these (e.g. because it is a
backend file), then these redefinitions can be disabled by #defining
FORBIDDEN_SYMBOL_ALLOW_ALL as the first thing in the .cpp file. Whenever
this is done, an explanatory comment should be added.

Note that this system cannot catch all "bad" usages (notably the Lua
code in the sword25 engine), as it can only work if scummsys.h is
included.

svn-id: r53961

backends/platform/sdl/sdl.cpp

@@ -23,6 +23,9 @@
  *
  */
 
+// Disable symbol overrides so that we can use system headers.
+#define FORBIDDEN_SYMBOL_ALLOW_ALL
+
 #if defined(WIN32)
 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
@@ -79,7 +82,7 @@
 #endif
 
 #if defined(MACOSX) || defined(IPHONE)
-#include "CoreFoundation/CoreFoundation.h"
+#include <CoreFoundation/CoreFoundation.h>
 #endif