missing setAccessToken

This missing line was causing problem when used with the following scenario:

```php
$facebookAdapter->getAccessToken();
//[...] some actions
$facebookAdapter->setExtendedAccessToken();
$facebookAdapter->getAccessToken();
```

there was an error

```
{"error":{"message":"Error validating verification code. Please make sure your redirect_uri is identical to the one you used in the OAuth dialog request","type":"OAuthException","code":100}}
```

Why? 
Because here:
https://github.com/facebook/facebook-php-sdk/blob/master/src/base_facebook.php#L382
session is destroyed.

and then here:
https://github.com/facebook/facebook-php-sdk/blob/master/src/base_facebook.php#L399
cached version of access token is not returned.

And then there is a request to exchange code to access token, but our code is expired.

This problem exists when we already passed the facebook authentication process and our url is like this:
```
http://example.com?code=CODE&state=STATE#_=_
```