+Tests to check if adapter passed in http_client_options gets correctly initialized

Hello, I hope these tests are useful. I've added three tests to check if the adapter passed in the http_client_options gets correctly initialized.

The first test `testAdapterAlwaysReachableIfSpecified` passes, but the other two don't. It seems there is some issue when passing `access_token`.

I got the problem while following the [documentation on Authentication](http://zf2.readthedocs.org/en/latest/modules/zendservice.twitter.html#authentication) where it says that this configuration can be used:

	$twitter = new ZendService\Twitter\Twitter(array(
	    'access_token' => array( // or use "accessToken" as the key; both work
	        'token' => 'your-access-token',
	        'secret' => 'your-access-token-secret',
	    ),
	    'oauth_options' => array( // or use "oauthOptions" as the key; both work
	        'consumerKey' => 'your-consumer-key',
	        'consumerSecret' => 'your-consumer-secret',
	    ),
	    'http_client_options' => array(
	        'adapter' => 'Zend_Http\Client\Adapter\Curl',
	    ),
	));