Correct Heimdal conversion of libadmin/adminutil

Correct Heimdal conversion of libadmin/adminutil

Patchset 4251e386aa25bb3fc02fa255e92327fffc8b954d converts to
using Heimdal.  The conversion undid the introduction of the
abstraction function fetch_krb5_error_message() which is
implemented in src/util.  Restore the use of fetch_krb5_error_message()
and modify src/util/krb5_nt.c to use the Kerberos Compat SDK
interface.

Change-Id: I67fe7a309727f67a1da3705e1e485e64747c325c
Reviewed-on: http://gerrit.openafs.org/5571
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>