[krbdev.mit.edu #7871] KDC should not fail requests due to forwardable/proxiable option

[Greg Hudson via RT]

If the client requests forwardable or proxiable tickets and the client or 
server DB entry has disallow-forwardable or disallow-proxiable set, we 
fail the request.  It would be more helpful to just issue a ticket 
without the forwardable/proxiable ticket flag set, as Heimdal and Active 
Directory do.