Move AudacityMessageBox to its own files...

... breaking cycles among low-level files introduced by 273ba9f

src/widgets/AudacityMessageBox.h

@@ -0,0 +1,28 @@
+/**********************************************************************
+
+  Audacity: A Digital Audio Editor
+
+  AudacityMessageBox.h
+
+  Paul Licameli split this out of ErrorDialog.h
+
+**********************************************************************/
+
+#ifndef __AUDACITY_MESSAGE_BOX__
+#define __AUDACITY_MESSAGE_BOX__
+
+#include <wx/msgdlg.h>
+
+extern wxString AudacityMessageBoxCaptionStr();
+
+// Do not use wxMessageBox!!  Its default window title does not translate!
+inline int AudacityMessageBox(const wxString& message,
+                              const wxString& caption = AudacityMessageBoxCaptionStr(),
+                              long style = wxOK | wxCENTRE,
+                              wxWindow *parent = NULL,
+                              int x = wxDefaultCoord, int y = wxDefaultCoord)
+{
+   return ::wxMessageBox(message, caption, style, parent, x, y);
+}
+
+#endif