Adding more cffi bindings to openssl backend.

- specifically adding items relating to X509 certificates.
Adding more cffi bindings to openssl backend.

- specifically adding items relating to X509 certificates.
Merge branch 'master' of https://github.com/callidus/cryptography

Conflicts:
	src/cryptography/hazmat/bindings/openssl/asn1.py
	src/cryptography/hazmat/bindings/openssl/evp.py
Making EVP_sha* bindings none conditional.

- these were added in OpenSSL 0.9.8, a supported version.
Moving things about to prevent compiler warnings with newer OpenSSL

- some of these bindings changed to const in various newer OpenSSL
  versions. Moving them to macros section to acccount for this
Merge pull request #1534 from callidus/master

Adding more X509 related cffi bindings