title: MS CRM 4 - Custom entity with "regardingobjectid" functionality
body: <p>I've made a custom entity that will work as an data modification audit (any entity modified will trigger creating an instance of this entity). So far I have the plugin working fine (tracking old and new versions of properties changed).</p>
  
  <p>I'd like to also keep track of what entity this is related to. At first I added a N:1 from DataHistory to Task (eg.) and I can indeed link back to the original task (via a "new_tasksid" attribute I added to DataHistory).</p>
  
  <p>The problem is every entity I want to log will need a separate attribute id (and an additional entry in the form!)</p>
  
  <p>Looking at how phone, task, etc utilize a "regardingobjectid", this is what I should do. Unfortunately, when I try to add a "dataobjectid" and map it to eg Task and PhoneCall, it complains (on the second save), that the reference needs to be unique. How does the CRM get around this and can I emulate it?</p>