title: Lithium framework multiple 'or' statements in a query (using mongoDB)
body: <p>I have started work with lithium framework + mongoDB recently. I want to do a really simple query which contains multiple or statements.
  I have articles in the DB with publish_up and publish_down fields. I want to fetch only those records/documents which pulbis_down field is highert than now OR null AND publish_up field lower than now OR null.</p>
  
  <pre><code>$items = $article::find('all', array(
      'conditions' =&gt; array(
          '$or' =&gt; array(
              '$gt' =&gt; array('publish_down', $mongoDateNow),
              'publish_down' =&gt; $mongDateNull
          ),
          '$or' =&gt; array(
              '$lt' =&gt; array('publish_up', $mongoDateNow),
              'publish_up' =&gt; $mongDateNull
          ),
      )
  ));
  </code></pre>
  
  <p>Of course this snippet is wrong hence the second or statement overwrites the first one (because the same array key).
  I tried to wrap them into an individual array but gives error.
  Any idea?</p>