kdb5_util load mix-in operation

[Will Fiveash]

In order to make the krb5_ldap_put_principal() more efficient when doing
a kdb5_util load I am requiring that if the user wants krb principals to
be mixed in with existing non-krb entries then they will need to use a
-x mixin arg like so:

kdb5_util load -update -x mixin <dump-file>

and they must add the krbprincipalname attribute with principal name
value to mix-in entries prior to the load.  The user will also have to
set, prior to the load, the subtrees attribute in the realm entry such
that the mix-in entry can be found under one of the subtrees.  If a
mix-in entry is located with the matching krbprincipalname attribute
that entry is modified with the krb princ aux. attributes from the dump
record.  If a mix-in entry can not be found then a standalone krb princ
entry will be created under the realm container.

If they do not provide the -x mixin arg then all krb princ will be
created as standalone krb princ entries.  This will avoid a needless
search for the mix-in entry.
-- 
Will Fiveash
Sun Microsystems Inc.
Austin, TX, USA (TZ=CST6CDT)