r19604: This is a massive commit, and I appologise in advance for it's size.

r19604: This is a massive commit, and I appologise in advance for it's size.

This merges Samba4 with lorikeet-heimdal, which itself has been
tracking Heimdal CVS for the past couple of weeks.

This is such a big change because Heimdal reorganised it's internal
structures, with the mechglue merge, and because many of our 'wishes' have been granted:  we now have DCE_STYLE GSSAPI, send_to_kdc hooks and many other features merged into the mainline code.  We have adapted to upstream's choice of API in these cases.

In gensec_gssapi and gensec_krb5, we either expect a valid PAC, or NO
PAC.  This matches windows behavour.  We also have an option to
require the PAC to be present (which allows us to automate the testing
of this code).

This also includes a restructure of how the kerberos dependencies are
handled, due to the fallout of the merge.

Andrew Bartlett