Added $_COOKIE to RequestSet environment.
Plugins like "plugin-QueuedTracking" need this change, because they process requests asynchronously (not with the same PHP context).
Travis CI failes because of the setEnvironment() calls in the tests for "plugin-QueuedTracking". These errors will be fixed with another pull request for "plugin-QueuedTracking". I will link it here, once it exists.
Thank you for your pull request! We're glad you are contributing to Piwik. Do you know when you will be creating the PR in QueuedTracking plugin? Looking forward to the other PR and reviewing them both. Cheers
Thank you for your feedback!
It took a bit longer than expected, because in order to update the tests, I also had to modify piwik-php-tracker. But the patches should be ready in one or two days now.