Add support for SSL version.

With the current version of SSL used by the requests library (SSLv23), the connection with the MELI webservice will drop with a timeout.

This fix it. 
How? Selecting a (and is configured with) SSL version that works (SSLv3).

Bug from OPENSSL:
http://askubuntu.com/questions/116020/python-https-requests-urllib2-to-some-sites-fail-on-ubuntu-12-04-without-proxy