Don't include krb5_kdc_req->from if default start time

[Greg Hudson]

On 05/14/2012 02:41 PM, Sam Hartman wrote:
>>>>>> "Greg" == Greg Hudson <ghudson at MIT.EDU> writes:
> 
>     Greg> Our KDC and Heimdal's KDC actually ignore the request's start
>     Greg> time unless the request includes the postdated option.  So I
>     Greg> think it's reasonable for krb5_get_init_creds to omit the
>     Greg> start time if (1) start_time is 0, and (2) options->flags does
>     Greg> not include KRB5_GET_INIT_CREDS_OPT_PROXIABLE.  I don't think
>     Greg> we even need to check for KRB5_LIBOPT_SYNC_KDCTIME.
> 
> What does proxiable have to do with it?

I thought I was pasting KRB5_GET_INIT_CREDS_OPT_POSTDATED.  But that
option turns out not to exist; postdating is implied by passing a
start_time greater than 0.

The patch I actually committed simply omits the from field if start_time
is 0.