Reuse previous ssl session

Version 0.1.1 has an issue when connecting to FTPS servers that are required to exhibit SSL session reuse.  When retrieving a file after connecting, the following message appears:

    522 SSL connection failed; session reuse required: see require_ssl_reuse 
    option in vsftpd.conf man page (Net::FTPPermError)

I copied this fix from https://github.com/alain75007/double-bag-ftps/commit/5aefbb7daeb24173993467326763fbf24ae72d39 since that fork doesn't seem to work with Ruby 2.0.