Add client_ca method to OpenSSL::SSLSocket
Please add "client_ca" method to OpenSSL::SSLSocket to solve the following problem.
If a SSL server decide to authenticate clients using client-certificates,
the server can send the list of client CAs to a client as a hint, and
the client can use the list to select an appropriate certificate.
But the current ruby's ext/openssl does not have the API to access the list.
Add a wrapper function for SSL_get_client_CA_list.
Two patches (new method and test) are attached to this message.