Here is a ridiculously stupid patch that fixes the behaviour to be 
closer to what I want.

Now, if the krb5 ticket has expired processes get a EKEYEXPIRED error 
and the kernel doesn't waste its time printing "ticket expired" errors.

 From the point of view of someone who has their home directory nfs 
mounted they go home after work, when they get back in the morning they 
give their password to the screensaver, pam_krb5 gets a new ticket and 
everything works.

(Without this hack the screensaver hangs before presenting the password 
prompt, presumably accessing something in the home directory).

Anyone care to comment?