Plaintext DSA test keys from GnuTLS

https://gitorious.org/gnutls/gnutls/commit/ad2061deafdd7db78fd405f9d143b0a7c579da7b
Add NIST FIPS 186-2 DSA test vectors

http://csrc.nist.gov/groups/STM/cavp/documents/dss/186-2dsatestvectors.zip
Add the FIPS 186-3 DSA test vectors

http://csrc.nist.gov/groups/STM/cavp/documents/dss/186-3dsatestvectors.zip
DSA test vector docs
Merge pull request #709 from public/dsa-test-vectors

DSA test vectors
new tox docs-linkcheck target for a jenkins job to do linkcheck
Merge pull request #715 from reaperhulk/add-linkcheck-target-to-tox

New tox docs-linkcheck target for a jenkins job to do linkcheck