Ensure high code coverage (now: 77.25%)

[aik099]

Main issue: https://github.com/Behat/Mink/issues/406

Code Coverage: 77.25%

[stof]

the coverage was increased a bit (approx 85% IIRC), and then #46 made it drop again as the test does not run through the code converting HttpFoundation responses to BrowserKit ones (which becomes a BC layer only). Running the tests on Symfony 2.2 would report a higher code coverage than on 2.3+ because of this.
Thanks to the removal of the BC layers in #44 for the 2.x branch, the coverage reaches 91%. Most of the remaining uncovered cases are actually safeguards throwing an error for invalid usage (some of them are probably hard to reach when using the driver through the higher level API of the element IMO)

[stof]

sorry, I wanted to close the GoutteDriver issue

[stof]

We now have 82% coverage, and 97% in the PR for 2.0 after removing the support of legacy Symfony versions. Closing this issue