Each .cpp/.mm file includes corresponding header before any other...

... except Audacity.h

This forces us to make each header contain all forward declarations or nested
headers that it requires, rather than depend on context.

src/RealFFTf.cpp

@@ -37,6 +37,7 @@
 */
 
 #include "Audacity.h"
+#include "RealFFTf.h"
 
 #include "Experimental.h"
 
@@ -47,7 +48,6 @@
 
 #include <wx/thread.h>
 
-#include "RealFFTf.h"
 #ifdef EXPERIMENTAL_EQ_SSE_THREADED
 #include "RealFFTf48x.h"
 #endif