Fix bug 387

Mac and Linux (correctly) allow files to be saved with an arbitrary
file extension, or no file extension at all. For the exported file
to be visible in the export dialog, the dialog must include an optional
wildcard for "All files".

src/FreqWindow.cpp

@@ -1054,8 +1054,13 @@ void FreqWindow::OnExport(wxCommandEvent & WXUNUSED(event))
    wxString fName = _("spectrum.txt");
 
    fName = FileNames::SelectFile(FileNames::Operation::Export,
-      _("Export Spectral Data As:"),
-      wxEmptyString, fName, wxT("txt"), wxT("*.txt"), wxFD_SAVE | wxRESIZE_BORDER, this);
+                                 _("Export Spectral Data As:"),
+                                 wxEmptyString,
+                                 fName,
+                                 wxT("txt"),
+                                 _("Text files (*.txt)|*.txt|All files|*"),
+                                 wxFD_SAVE | wxRESIZE_BORDER,
+                                 this);
 
    if (fName.empty())
       return;

src/effects/Contrast.cpp

@@ -509,7 +509,7 @@ void ContrastDialog::OnExport(wxCommandEvent & WXUNUSED(event))
                         wxEmptyString,
                         fName,
                         wxT("txt"),
-                        wxT("*.txt"),
+                        _("Text files (*.txt)|*.txt|All files|*"),
                         wxFD_SAVE | wxRESIZE_BORDER,
                         this);