Eliminate MSVC compiler warnings.Clean up some issues with Effect abstract classes, primarily that the progress dialog had Stop and Cancel buttons that produced exactly the same results, i.e., Cancel, so I removed the Stop button.

src/Dependencies.cpp

@@ -21,6 +21,7 @@
 
 **********************************************************************/
 
+#include <wx/button.h>
 #include <wx/defs.h>
 #include <wx/dialog.h>
 #include <wx/filename.h>

src/export/ExportCL.cpp

@@ -15,6 +15,7 @@
 
 #include "../Audacity.h"
 
+#include <wx/button.h>
 #include <wx/log.h>
 #include <wx/process.h>
 #include <wx/textctrl.h>