[krbdev.mit.edu #8814] Listing third-party KDC modules

I am not sure what the Samba roadmap entry is referring to.  The MIT 
KDC has supported within-realm S4U2Self since release 1.8.  In release 
1.17, the KDC supports cross-realm S4U2Self, if the KDB module issues 
appropriate realm referrals.  This KDC work was done by a Samba 
developer, so it is my understanding that the Samba KDB module can 
issue those referrals.

(There is another S4U2Self case where the client is identified by X.509 
certificate instead of principal name.  This case will be supported in 
release 1.18, provided that the KDB module implements a new lookup 
function.)