node.js is, effectively, another bindings library. However, it's better
written than most and, with these changes, only a couple of tiny fixes
are needed in node.js. Some of these changes are a little depressing
however so we'll need to push node.js to use APIs where possible.

Changes:
  ∙ Support verify_recover. This is very obscure and the motivation
    appears to be https://github.com/nodejs/node/issues/477 – where it's
    not clear that anyone understands what it means :(
  ∙ Add a few, no-op #defines
  ∙ Add some members to |SSL_CTX| and |SSL| – node.js needs to not
    reach into these structs in the future.
  ∙ Add EC_get_builtin_curves.
  ∙ Add EVP_[CIPHER|MD]_do_all_sorted – these functions are limited to
    decrepit.

Change-Id: I9a3566054260d6c4db9d430beb7c46cc970a9d46
Reviewed-on: https://boringssl-review.googlesource.com/6952
Reviewed-by: Adam Langley <agl@google.com>