handle MS PACs that lack server checksum

handle MS PACs that lack server checksum

target_version 1.9
tags: pullup

Apple Mac OS X Server's Open Directory KDC issues MS PAC like
authorization data that lacks a server checksum.  If this checksum is
missing, mark the PAC as unverfied, but allow
krb5int_authdata_verify() to succeed.  Filter out the unverified PAC
in subsequent calls to krb5_authdata_get_attribute().  Add trace
points to indicate where this behavior occurs.

Thanks to Helmut Grohne for help with analysis.  This bug is also
Debian Bug #604925:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=604925

This change should also get backported to krb5-1.8.x.

ticket: 6839

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@24564 dc483132-0cff-0310-8789-dd5450dbe970