Diffie-Hellman support in crypto module

[havard]

I've implemented Diffie-Hellman support in the crypto module, utilizing OpenSSL. Would you consider the patch for inclusion? I am uncertain as to whether you require more information than this pull request. If so, please let me know.

[ry]

Can you add a test?

[havard]

Let me know if you need anything else.

[ry]

Sorry, can you please fix the style. In particular the long lines:

python tools/cpplint.py src/node_crypto.cc

Please start with this patch: https://gist.github.com/815320

• I removed the addition to AUTHORS, which we do when we bump the version
• Rebased to master
• fixed the long lines in the docs

[havard]

Same commit as patch ready for application on top of your rebased patch: https://gist.github.com/817133. Or, you can cherry-pick the last commit (which was cherry-picked onto master from a branch started from your rebased patch).