Include nothing before Audacity.h, as comments say we should...

... and remove some duplicated inclusions

src/ondemand/ODDecodeTask.cpp

@@ -18,6 +18,7 @@ updating the ODDecodeBlockFile and the GUI of the newly available data.
 
 #include "../Audacity.h"
 #include "ODDecodeTask.h"
+
 #include "../blockfile/ODDecodeBlockFile.h"
 #include "../Sequence.h"
 #include "../WaveTrack.h"

src/ondemand/ODManager.cpp

@@ -16,6 +16,7 @@ ODTask requests and internals.
 
 #include "../Audacity.h"
 #include "ODManager.h"
+
 #include "ODTask.h"
 #include "ODTaskThread.h"
 #include "ODWaveTrackTaskQueue.h"

src/ondemand/ODTaskThread.h

@@ -21,9 +21,11 @@
 
 #ifndef __AUDACITY_ODTASKTHREAD__
 #define __AUDACITY_ODTASKTHREAD__
-#include <wx/thread.h>
 
 #include "../Audacity.h"	// contains the set-up of AUDACITY_DLL_API
+
+#include <wx/thread.h>
+
 #include "../MemoryX.h"
 
 class ODTask;

src/ondemand/ODWaveTrackTaskQueue.cpp

@@ -18,6 +18,7 @@ tasks associated with a WaveTrack.
 
 #include "../Audacity.h"
 #include "ODWaveTrackTaskQueue.h"
+
 #include "ODTask.h"
 #include "ODManager.h"
 #include "../WaveTrack.h"