Fix exception handling in Boris CLI

The new Boris integration is great, but the Laravel exception handlers interfere with it. For example if you type an undefined constant it quits with an exception:

```
$ art tinker
[1] > d;



  [ErrorException]
  Use of undefined constant d - assumed 'd'



tinker

$
```

This PR disables all the Laravel exception handlers so Boris can handle them correctly:

```
$ art tinker
[1] > d;
PHP Notice:  Use of undefined constant d - assumed 'd' in /home/www/intranet.kes.davejamesmiller.com/repo/vendor/d11wtq/boris/lib/Boris/EvalWorker.php(133) : eval()'d code on line 1
PHP Stack trace:
PHP   1. {main}() /home/www/intranet.kes.davejamesmiller.com/repo/artisan:0
PHP   2. Symfony\Component\Console\Application->run() /home/www/intranet.kes.davejamesmiller.com/repo/artisan:59
PHP   3. Symfony\Component\Console\Application->doRun() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/symfony/console/Symfony/Component/Console/Application.php:124
PHP   4. Symfony\Component\Console\Application->doRunCommand() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/symfony/console/Symfony/Component/Console/Application.php:194
PHP   5. Illuminate\Console\Command->run() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/symfony/console/Symfony/Component/Console/Application.php:888
PHP   6. Symfony\Component\Console\Command\Command->run() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/laravel/framework/src/Illuminate/Console/Command.php:96
PHP   7. Illuminate\Console\Command->execute() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/symfony/console/Symfony/Component/Console/Command/Command.php:245
PHP   8. Illuminate\Foundation\Console\TinkerCommand->fire() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/laravel/framework/src/Illuminate/Console/Command.php:108
PHP   9. Illuminate\Foundation\Console\TinkerCommand->runBorisShell() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/laravel/framework/src/Illuminate/Foundation/Console/TinkerCommand.php:30
PHP  10. Boris\Boris->start() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/laravel/framework/src/Illuminate/Foundation/Console/TinkerCommand.php:56
PHP  11. Boris\EvalWorker->start() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/d11wtq/boris/lib/Boris/Boris.php:171
PHP  12. eval() /home/www/intranet.kes.davejamesmiller.com/repo/vendor/d11wtq/boris/lib/Boris/EvalWorker.php:133
 → 'd'
[2] > 
```

(The code is copied from my [Laravel Boris](https://github.com/davejamesmiller/laravel-boris) package for 4.0.)