[krbdev.mit.edu #2656] krb5_get_init_creds() should support ticket_lifetime libdefault

[Alexandra Ellwood via RT]

krb5_get_init_creds() should support ticket_lifetime libdefault.  Because everyone seems to 
expect it to be named that (from looking at mail) and it's kindof dumb to have a 
renew_lifetime libdefault and not have one for the ticket lifetime.