Change KRB5_AUTHDATA_SIGNTICKET from 142 to 512

Change KRB5_AUTHDATA_SIGNTICKET from 142 to 512

KRB5_AUTHDATA_SIGNTICKET, originally a Heimdal authorization data
type, was used to implement PAC-less constrained delegation in krb5
1.8.  Unfortunately, it was found that Microsoft was using 142 for
other purposes, which could result in a ticket issued by an MIT or
Heimdal KDC being rejected by a Windows Server 2008 R2 application
server.  Because KRB5_AUTHDATA_SIGNTICKET is only used to communicate
among a realm's KDCs, it is relatively easy to change the number, so
MIT and Heimdal are both migrating to a new number.  This change will
cause a transitional interoperability issue when a realm mixes MIT
krb5 1.8 (or Heimdal 1.3.1) KDCs with MIT krb5 1.8.1 (or Heimdal
1.3.2) KDCs, but only for constrained delegation evidence tickets.

ticket: 6687
target_version: 1.8.1
tags: pullup

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@23821 dc483132-0cff-0310-8789-dd5450dbe970