title: Querying Salesforce ContentDocumentLink from trigger returns incomplete response
body: <p>Working on a trigger to send notifications when a specific user uploads Files/ContentDocuments to a Case.  From ContentVersion I retrieve the ContentDocument.Ids, which I pass into a method to retrieve ContentDocumentLinks:</p>
  <pre><code>    ContentDocumentLink[] results;
      results = [
          SELECT ContentDocumentId, ContentDocument.OwnerId, LinkedEntityId 
          FROM   ContentDocumentLink 
          WHERE  ContentDocumentId IN :oContentDocumentIds order by LinkedEntityId desc];
  </code></pre>
  <p>If I query (vs. calling the method) using a known ContentDocument.Id in anonymous apex it returns two ContentDocumentLinks - one linking the File to the User, and one linking the File to the Case.  When called from the ContentVersion trigger, it only returns the one linking to the User.  It doesn't appear to be a sharing issue, since if I have the permissions to attach a File to a Case, I should have access to the ContentDocumentLink associating the File to the Case.</p>