Echo KDC cookies in preauth tryagain

When trying again after a mechanism-specific error, we should send the
KDC cookie for conformance with RFC 6113.

https://github.com/krb5/krb5/commit/25f12e90d98b677d0a72893b3c6eb859377aee68
Author: Greg Hudson <ghudson@mit.edu>
Commit: 25f12e90d98b677d0a72893b3c6eb859377aee68
Branch: master
 src/lib/krb5/krb/preauth2.c |    8 +++++++-
 src/tests/t_pkinit.py       |    6 ++++--
 2 files changed, 11 insertions(+), 3 deletions(-)