title: Unable to include and exclude fields of query via mongoose
body: <p>I have some schema and making query as following :</p>
  
  <pre><code>mongoose.model('mymodel').find({}, 'one -two -__v', function(err,docs){});
  </code></pre>
  
  <p>I want documents should only return the field 'one'. Always ignore the fields 'two' and rest all.
  Then i get the following error :</p>
  
  <pre><code>You cannot currently mix including and excluding fields. Contact us if this is an issue.
  </code></pre>
  
  <p>I am generating the field string dynamically to include or exclude the fields required.</p>
  
  <p>How to get rid of the error.</p>