allow to verify ssl connections against a CA.

allow to verify ssl connections against a CA.

This adds three new configuration variables to configure
SSL verification against a CA.

server.ssl_verify: true if it should verify and disconnect
                   if it fails

server.ssl_ca_file: a CA file, is set to the systems CA
                    bundle by default (distri. dependent)

server.ssl_ca_path: alternativly path to a directory with
                    CA PEM files

I tested it and this seems no longer an issue with >= 1.9.3
https://www.braintreepayments.com/braintrust/sslsocket-verify_mode-doesnt-verify