[Http] Checks and uses $config['adapter'] when current adapter is not usable

I'm followind the [Authentication](http://zf2.readthedocs.org/en/latest/modules/zendservice.twitter.html#authentication) and the [Seach Methods](http://zf2.readthedocs.org/en/latest/modules/zendservice.twitter.html#search-methods) documentation for `ZendService\Twitter`.

Using the following configuration and running the `PHP` script at the bottom I get this error:

    PHP Fatal error:  Call to a member function connect() on a non-object in /Users/me/test/vendor/zendframework/zend-http/Zend/Http/Client.php on line 1358

The `composer.json`:

    {
        "require":
        {
            "zendframework/zendservice-twitter": "dev-master"
        }
    }

Running `composer.phar update`
    
    Loading composer repositories with package information
    Installing dependencies (including require-dev)
      - Installing zendframework/zend-stdlib (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-validator (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-escaper (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-uri (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-math (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-i18n (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-loader (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-http (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-servicemanager (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-crypt (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-config (2.2.5)
        Loading from cache
    
      - Installing zendframework/zendoauth (2.0.2)
        Loading from cache
    
      - Installing zendframework/zend-json (2.2.5)
        Loading from cache
    
      - Installing zendframework/zend-feed (2.2.5)
        Loading from cache
    
      - Installing zendframework/zendservice-twitter (dev-master f20c772)
        Cloning f20c772e791015aef9f89411f61131465b918337
    
    zendframework/zend-stdlib suggests installing zendframework/zend-eventmanager (To support aggregate hydrator usage)
    zendframework/zend-validator suggests installing zendframework/zend-db (Zend\Db component)
    zendframework/zend-validator suggests installing zendframework/zend-filter (Zend\Filter component, required by the Digits validator)
    zendframework/zend-validator suggests installing zendframework/zend-resources (Translations of validator messages)
    zendframework/zend-math suggests installing ircmaxell/random-lib (Fallback random byte generator for Zend\Math\Rand if OpenSSL/Mcrypt extensions are unavailable)
    zendframework/zend-i18n suggests installing ext-intl (Required for most features of Zend\I18n; included in default builds of PHP)
    zendframework/zend-i18n suggests installing zendframework/zend-eventmanager (You should install this package to use the events in the translator)
    zendframework/zend-i18n suggests installing zendframework/zend-filter (You should install this package to use the provided filters)
    zendframework/zend-i18n suggests installing zendframework/zend-view (You should install this package to use the provided view helpers)
    zendframework/zend-i18n suggests installing zendframework/zend-resources (Translation resources)
    zendframework/zend-servicemanager suggests installing zendframework/zend-di (Zend\Di component)
    zendframework/zend-json suggests installing zendframework/zend-server (Zend\Server component)
    Writing lock file
    Generating autoload files

The `PHP` file using `ZendService\Twitter`:
    
    <?php
    include "vendor/autoload.php";
    
    $config = array(
        'access_token' => array(
            'token'  => 'TWITTER_TOKEN',
            'secret' => 'TWITTER_SECRET',
        ),
        'oauth_options' => array(
            'consumerKey' => 'TWITTER_CONSUMER_KEY',
            'consumerSecret' => 'TWITTER_CONSUMER_SECRET',
        ),
        'http_client_options' => array(
            'adapter' => 'Zend\Http\Client\Adapter\Curl',
        ),
    );
    
    $twitter = new \ZendService\Twitter\Twitter($config);
    
    $response = $twitter->search->tweets('#zf2');
    $tweets = $response->statuses;
    var_dump($tweets);