Experimental.h in all .h or .cpp files that directly use EXPERIMENTALs...

... except Audacity.h; and in no others.

Do so even if Experimental.h gets multiply included, as in both the .h and
.cpp files.

This makes it easier to do a text scan to be sure there are no unintended quiet
changes of meaning because of omission of Experimental.h when the flag is
an enabled one.

Also move inclusions of Experimental.h earlier.

Also don't require Experimental.h to be preceded by Audacity.h to define
EXPERIMENTAL_MIDI_OUT correctly.

src/ondemand/ODDecodeFFmpegTask.cpp

@@ -11,6 +11,8 @@
 
 #include "../Audacity.h"   // needed before FFmpeg.h
 
+#include "../Experimental.h"
+
 #include <wx/wxprec.h>
 // For compilers that support precompilation, includes "wx/wx.h".
 #ifndef WX_PRECOMP
@@ -18,8 +20,6 @@
 #include <wx/window.h>
 #endif
 
-#include "../Experimental.h"
-
 #ifdef USE_FFMPEG
 #ifdef EXPERIMENTAL_OD_FFMPEG
 

src/ondemand/ODDecodeFFmpegTask.h

@@ -13,6 +13,7 @@
 #define __ODDECODEFFMPEGTASK__
 
 #include "../Experimental.h"
+
 #include "../MemoryX.h"
 
 #ifdef EXPERIMENTAL_OD_FFMPEG