r21822: Adding experimental krb5 lib locator plugin.

r21822: Adding experimental krb5 lib locator plugin.

This is a starting point and may get changed. Basically we need follow the
exact same path to detect (K)DCs like other Samba tools/winbind do. In
particular with regard to the server affinity cache and the site-awarness for
DNS SRV lookups.

To compile just call "make bin/smb_krb5_locator.so", copy to
/usr/lib/plugin/krb5/ (Heimdal HEAD) or /usr/lib/krb5/plugins/libkrb5/ (MIT)
and you should immediately be able to kinit to your AD domain without having
your REALM with kdc or kpasswd directives defined in /etc/krb5.conf at all.

Tested with todays Heimdal HEAD and MIT krb5 1.5.

Guenther