Test with SSL on Travis
Use /dev/null in invalidate_fd to avoid infinite loop in OpenSSL

Thanks to Andy Bakun / @thwarted for identifying the issue and
suggesting the /dev/null workaround.
change sql_state to attr_reader to avoid ruby warning
Merge pull request #544 from seuros/master

change sql_state to attr_reader to avoid ruby warning
Merge pull request #535 from sodabrew/travis_ssl

Enable SSL tests on Travis