(svn r2685) -Codechange: Split the music/sound/video drivers into separate files and move them into subfolders.

This results in shorter and hopefully easier to maintain files.
Note: I had to change paths in #include statements of some unrelated files, because I added the ottd base directory to the include path (-I.)

os/beos/bemidi.cpp

@@ -1,55 +0,0 @@
-#ifdef __BEOS__
-
-#include "stdafx.h"
-#include "openttd.h"
-#include "hal.h"
-
-// BeOS System Includes
-#include <MidiSynthFile.h>
-
-BMidiSynthFile midiSynthFile;
-
-static const char *bemidi_start(const char * const *parm)
-{
-	return NULL;
-}
-
-static void bemidi_stop(void)
-{
-	midiSynthFile.UnloadFile();
-}
-
-static void bemidi_play_song(const char *filename)
-{
-	bemidi_stop();
-	entry_ref midiRef;
-	get_ref_for_path(filename, &midiRef);
-	midiSynthFile.LoadFile(&midiRef);
-	midiSynthFile.Start();
-}
-
-static void bemidi_stop_song(void)
-{
-	midiSynthFile.UnloadFile();
-}
-
-static bool bemidi_is_playing(void)
-{
-	return !midiSynthFile.IsFinished();
-}
-
-static void bemidi_set_volume(byte vol)
-{
-	fprintf(stderr, "BeMidi: Set volume not implemented\n");
-}
-
-const HalMusicDriver _bemidi_music_driver = {
-	bemidi_start,
-	bemidi_stop,
-	bemidi_play_song,
-	bemidi_stop_song,
-	bemidi_is_playing,
-	bemidi_set_volume,
-};
-
-#endif // __BEOS__