[Xfce] Disable session saving on shutdown or logout

Xfce can save the current session on shutdown or logout so that the next time the user logs in, all the applications he was using are up and running. Unfortunately, this setting sometimes is enabled even when not requested; to change it, edit ~/.config/xfce4/xfconf/xfce-perchannel-xml/xfce4-session.xml by setting these properties:

 <property name="AutoSave" type="bool" value="false"/>  
 <property name="SaveOnExit" type="bool" value="false"/>