Keep cause error of KeepAliveDisconnected

Allow caller to investigate the cause of KeepAliveDisconnected.
Update default SSL configuration

 * Disable SSLv3 in favor of POODLE Attach prevention.
 * Enable 1/n-1 fragment in favor of BEAST Attach prevention.
 * No TLS compression in favor of CRIME Attach prevention.

You can restore the previous SSL configuration like this;
```ruby
client = HTTPClient.new
client.ssl_config.ssl_version = :SSLv23
client.ssl_config.options = OpenSSL::SSL::OP_ALL | OpenSSL::SSL::OP_NO_SSLv2
```