Use new socket if uid, pid, or gid changes
    
    The gssproxy daemon uses SO_PEERCRED to determine credentials of the
    connecting process.  However, these credentials are set only at the time
    connect has called.  Therefore they must be reset every time uid or pid
    changes.  For completeness, we check gid as well.
    
    Signed-off-by: Robbie Harwood <rharwood@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Closes #27