Make it possible to set the external file browser on unix.

xdg-open is not available everywhere and fails when no DE is running.

Reviewed-By: Oswald Buddenhagen

src/plugins/coreplugin/generalsettings.h

@@ -62,10 +62,15 @@ private slots:
     void resetExternalEditor();
     void showHelpForExternalEditor();
 #ifdef Q_OS_UNIX
+#  ifndef Q_OS_MAC
+    void showHelpForFileBrowser();
+    void resetFileBrowser();
+#  endif
     void resetTerminal();
 #endif
 
 private:
+    void variableHelpDialogCreator(const QString& helpText);
     Ui::GeneralSettings *m_page;
     QString m_searchKeywords;
     QPointer<QWidget> m_dialog;