Provide basic integration testing with Request and Response objects.

This is a proposal for a skeleton `TestCase` that would be used to do integration testing with Kohana application.

I managed to test my application by self-requesting using internal `Request` just like the following:
```php
$response = Request::factory('some/internal/endpoint')
    ->method(Request::POST)
    ->post('key', 'value')
    ->execute();

$this->assertEquals(200, $response->status(), $response->body());
```

But this gets a little messy and a lot of work has to be duplicated (especially for other status codes).

What I propose is a simple `TestCase_Integration` that would provide primitives for testing `Response` objects, making building and testing quality application simpler.
```php
$this->assertOk($response);
$this->assertPermanentRedirect('http://some/location', $response);
```

I would like to have your insights on the matter!
I think this would be better as a first-class PHPUnit assertion, so that if it fails it can show the whole of the status/location header/etc in a useful failure message that describes the overall assertion and what was incorrect, rather than a chain of assertEquals.

For example, `Expected 200 to equal 301 but it did not` doesn't tell you whether the Location header was set or not, so you don't know if the issue is that the application never redirected, or it did but the status code went wrong along the way.