SSL: Support ECDH key exchange (1/2)

https://commitfest.postgresql.org/action/patch_view?id=1286
http://archives.postgresql.org/message-id/20131115194951.GA19663@gmail.com
SSL: Support ECDH key exchange (2/2)

https://commitfest.postgresql.org/action/patch_view?id=1286
http://archives.postgresql.org/message-id/20131115194951.GA19663@gmail.com