r7270: A big revamp to the way we handle kerberos errors in Samba4. We now

r7270: A big revamp to the way we handle kerberos errors in Samba4.  We now
fill in the function pointers to handle the logging, and catch all the
kerberos warnings. (Currently at level 3).

To avoid a memory leak, this requries a new function: krb5_freelog(),
which I've added to lorikeet/heimdal.

This also required a revamp to how we handle the krb5_context, so as
to make it easier to handle with talloc destructors.

Andrew Bartlett
(This used to be commit 63272794c41231b335b73e7ccf349282f295c4d2)