Prototype encode_krb5_enc_tkt_part for aklog

Prototype encode_krb5_enc_tkt_part for aklog

Prototype encode_krb5_enc_tkt_part in aklog_main.c, since it is a
private interface so we don't get a prototype from the krb5 headers.

Reviewed-on: http://gerrit.openafs.org/680
Tested-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Derrick Brashear <shadow@dementia.org>