Allow portage fetch domain to show download progress
    
    When downloading software packages, the portage application is inside the
    portage_fetch_t domain. At that point, Portage wants to show the fetch progress
    of the software on the users' screen. For this, it needs proper access to
    portage_devpts_t.
    
    Signed-off-by: Sven Vermeulen <sven.vermeulen@siphos.be>