[krbdev.mit.edu #3266] Include errno.h in kdc/kerberos_v4.c

[Public Submitter via RT]

The following patch has been in the Debian Kerberos package for a while.
 My guess is that it's not strictly needed and that some other header
file happens to pull in errno.h, but I've confirmed that this file does
use the errno constants and doesn't otherwise include errno.h.