r21845: Refactor the sessionsetupX code a little to allow us

r21845: Refactor the sessionsetupX code a little to allow us
to return a NT_STATUS_TIME_DIFFERENCE_AT_DC error to
a client when there's clock skew. Will help people
debug this. Prepare us for being able to return the
correct sessionsetupX "NT_STATUS_MORE_PROCESSING_REQUIRED"
error with associated krb5 clock skew error to allow
clients to re-sync time with us when we're eventually
able to be a KDC.
Jeremy.
(This used to be commit c426340fc79a6b446033433b8de599130adffe28)