Bug fix: error messages don't work.

Hi Felix.  Great work on this much-needed super-useful validator.  

I noticed the wrong validator instance property was getting set for the source error message templates: $this->messages is for a MessageBag object representing the result of validation, i.e. it's returned by $this->messages().  The "$messages" parameter that is passed into Illuminate/Validation/Validator.php::__construct() gets assigned to $this->customMessages, not $this->messages.  So accessing $this->messages directly was a mistake.  

Also, since the constructor accepts this (custom error messages) as a parameter, there was no need to modify the instance member directly, so I changed it to pass this array into the constructor instead.

Also, I noticed the Illuminate/Validation/Validator::__construct method signature had an extra param that ValidatorExtension did not support.  So I added support for that as well.

The tests illustrate the problems I fixed.  They will fail without the patch to ValidatorExtension.  They succeed with it.  I also removed unnecessary calls to trans->shouldReceive since this is done already in setUp().  I also unbroke the returning of data for certain mocked translator calls, so the error messages can be seen in the tests now also.

Let me know if any questions.