[krbdev.mit.edu #6782] Master KDC lookup can use SRV lookups despite local realm KDC configuration

[Greg Hudson via RT]

If a realm is defined in the profile with one or more kdc values but no 
master_kdc variable is defined, krb5_sendto_kdc() will perform SRV 
lookups in order to determine the master KDC value, even if there's only 
one KDC defined.

It would be more admin-friendly and performant to use the first value of 
"kdc" in the profile as the master KDC.