Develop Kerberos renew system for ticket

Develop Kerberos renew system for ticket

    - In Preference pane has been added a tab called "Option" where are
      showned the option for kerberos renew
    - In AfsBackgrounder has been implemented the NSTimer that will call
      the krb5 renew action according to user preference value

Change-Id: Ica4b705018722488613ac09586e60c69303d1076
Change-Id: I79ce1334d99f926544e865fbb563a1ffecaa969c
Reviewed-on: http://gerrit.openafs.org/1606
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>