ModelNotFoundException() : include called class name

There is no way to know which model is throwing `ModelNotFoundException()`.
With this simple code change, the following is now possible:

```php
<?php
// routes.php

use Illuminate\Database\Eloquent\ModelNotFoundException;

Route::get('/dummy-package', function ()
{
	$package = Package::findOrFail('unknown_id')->toArray();

	return Response::view('package.show', array('package' => $package));
});

App::error(function (ModelNotFoundException $e, $code)
{
	$model = substr($e->getMessage(), 0, strpos($e->getMessage(), ':'));

	switch ($model)
	{
		case 'User':
			return Response::view('_errors.user_not_found', 404);

		case 'Project':
			return Response::view('_errors.project_not_found', 404);

		default:
			return Response::view('_errors.404', 404);
	}
});
```