s4:heimdal Allow KRB5_NT_ENTERPRISE names in all DB lookups

s4:heimdal Allow KRB5_NT_ENTERPRISE names in all DB lookups

The previous code only allowed an KRB5_NT_ENTERPRISE name (an e-mail
list user principal name) in an AS-REQ.  Evidence from the wild
(Win2k8 reportadely) indicates that this is instead valid for all
types of requests.

While this is now handled in heimdal/kdc/misc.c, a flag is now defined
in Heimdal's hdb so that we can take over this handling in future (once we start
using a system Heimdal, and if we find out there is more to be done
here).

Andrew Bartlett