Removed the old Behat configuration file

Mink does not use Behat anymore since we extracted the Behat
integration to a separate MinkExtension repo
Removed unused requirements relying on PHPUnit in the include path
Added tests for multiple checkboxes without id
Added another test to demonstrate that the BrowserKit fix is broken
Merge pull request #410 from stof/test_driver

Added tests for multiple checkboxes without id