(svn r2688) MSVC and Watcom can't handle identical file names in different directories, oh my...

sound/null_s.c

@@ -1,6 +1,6 @@
 #include "stdafx.h"
 #include "openttd.h"
-#include "sound/null.h"
+#include "sound/null_s.h"
 
 static const char *NullSoundStart(const char * const *parm) { return NULL; }
 static void NullSoundStop(void) {}

sound/sdl_s.c

@@ -3,7 +3,7 @@
 #include "driver.h"
 #include "mixer.h"
 #include "sdl.h"
-#include "sound/sdl.h"
+#include "sound/sdl_s.h"
 #include <SDL.h>
 
 static void CDECL fill_sound_buffer(void *userdata, Uint8 *stream, int len)

sound/win32_s.c

@@ -3,7 +3,7 @@
 #include "driver.h"
 #include "functions.h"
 #include "mixer.h"
-#include "sound/win32.h"
+#include "sound/win32_s.h"
 #include <windows.h>
 
 static HWAVEOUT _waveout;