add NIST PKITS X.509 vectors

We'll start using parts of this suite shortly.

http://csrc.nist.gov/groups/ST/crypto_apps_infra/pki/pkitesting.html
http://csrc.nist.gov/groups/ST/crypto_apps_infra/documents/PKITS_data.zip
http://csrc.nist.gov/groups/ST/crypto_apps_infra/documents/PKITS.pdf

Validating this should be done by pulling the down the branch, grabbing the PKITS_data.zip, and running a diff.