title: customOperation and addRestangularMethod would not use BaseUrl in Restangular
body: <p>I've been trying to create a custom method named 'upVote' for a resource called 'posts', the posts api url is at "/rest/users/{username}/posts" while the url for the vote action is at "/rest/posts/{postId}/vote".</p>
  
  <p>I have added the following configuration:</p>
  
  <pre><code>RestangularProvider.setBaseUrl(Routing.getBaseUrl() + '/rest');
  RestangularProvider.addElementTransformer('posts', false, function(post) {
       post.addRestangularMethod('upVote', 'patch', 'vote', {_token: ajaxToken}, {});
       return post;
  });
  </code></pre>
  
  <p>But the method sends the request to the wrong url (<code>/post/{postId}/vote</code>) and does not use the provided baseUrl at all.</p>
  
  <p>Is there a way to make the method use the configured baseUrl for it's requests, or am I doing this the wrong way?</p>