r4355: More work from the elves on Christmas eve:

r4355: More work from the elves on Christmas eve:

 - Update Samba4's kerberos code to match the 'salting' changes in
   Samba3 (and many other cleanups by jra).

 - Move GENSEC into the modern era of talloc destructors.  This avoids
   many of the memory leaks in this code, as we now can't somehow
   'forget' to call the end routine.
  - This required fixing some of the talloc hierarchies.

 - The new krb5 seems more sensitive to getting the service name
   right, so start actually setting the service name on the krb5 context.

Andrew Bartlett
(This used to be commit 278bf1a61a6da6ef955a12c13d7b1a0357cebf1f)