This routine fetches the next entry in the keytab, returning
it in *entry, and updates *cursor for
the next request. If the keytab changes during the sequential get,
an error is guaranteed. The argument *entry should
be freed after use by calling krb5_kt_free_entry.
This routine requires that id identifies
a valid keytab, and *cursor be a cursor
returned by krb5_kt_start_seq_get or a
subsequent call to krb5_kt_next_entry.