Update Autoconf Kerberos probes to latest rra-c-util version

Update Autoconf Kerberos probes to latest rra-c-util version

We will now look for krb5-config in /usr/kerberos/bin (the path used
on Red Hat Enterprise prior to RHEL6) if it isn't found in the user's
PATH.

This update also adds a new probe for krb5_get_init_creds_opt_free
which is not yet used, but may eventually be useful for klog.krb5.

Change-Id: Iefd67c02ac44fd5f1a30883d1cd6ea4e489b32b1
Reviewed-on: http://gerrit.openafs.org/2644
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit ae868642e1936509184cbe9b539733445902bdf3)
Reviewed-on: http://gerrit.openafs.org/2689