Massive changes to do_as_req.c, do_tgs_req.c, kdc_util.c, and policy.c

Massive changes to do_as_req.c, do_tgs_req.c, kdc_util.c, and policy.c
Fixed bug so that renewable/forwardable/proxiable/tickets work on all
tickets, not just the TGS server.  Fixed bug so that proxiable tickets
don't work on TGT tickets.

Revamped structure to make things cleaner, and easier to understand.  Nearly
all of the validation routines have been moved to a validate_as_request
and a validate_tgs_request subroutine in kdc_util.c.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@2451 dc483132-0cff-0310-8789-dd5450dbe970