Handle PAM session and account stack

[rhopfer]

At the moment it seams i3lock only handle the auth stack.

If pam_krb5 is used for authentication, the auth stack stores the credentials in a temprary file (/tmp/krb5_pam_XXXXXX). During session stack (pam_sm_setcred), the credentials are moved to its final location (/tmp/krb5cc_UID_XXXXXX) and the environment variable KRB5CCNAME will be set.

[stapelberg]

Can you send a pull request which makes the necessary changes please? I don’t have Kerberos set up in my environments anymore, so it would go a long way if you could send the PR :).