Able to start sessions as guest for special methods

Some methods need a session to dispatch correct. (eg customer/account/loginPost)
Instead of fixing the dispatch method I wrote a guest session.
This sets the needed $_GET[session_name] = session_id to have a successfull call for such "loginPost" actions.

This:

```
        $this->dispatch('customer/account/loginPost');

        $this->assertRequestRoute('customer/account/loginPost');
```

Will fail with:

```
Failed asserting that request route matches expected one.
--- Expected
+++ Actual
@@ @@
-'core/index/noCookies'
+'customer/account/loginPost'
```

And this is the fix:

```
        $this->guestSession();
        $this->dispatch('customer/account/loginPost');

        $this->assertRequestRoute('customer/account/loginPost');
```

Excuse the indention in config.xml this was the auto code format during the commit.