Fixed Undefined offset Notice on line 72 when not passing a valid magento connect 2.0 package.
Improvements on validation of magento 2.0 modules. On Ubuntu for example, when typing http://... the  turns on 2 dimensions array because of the ':' sign that splits the url causing the wiz mc-dl error (not a valid magento 2.0 package).
Applied same fix that @r-martins did on mc-versions to the error report in mc-dl.
Resolves #17. Merge pull request from r-martins/master with minor modification to resolve same notice in mc-dl.