title: How to listen to changes in all mongoDB collection
body: <p>I'm writing a meteor app,
  I would like to write an observer which will listen to changes on a remote mongoDB,
  Though I would like to write somthing generic which will listen to all Collections and will send the old value and new value. I mean:</p>
  
  <pre><code>var DBCollections = new Meteor.Collection.getall();  -&gt; whats the right way to do this?
  
  var cursor = DBCollection.find();
  
  
  // watch the cursor for changes
  var handle = cursor.observe({
    added: function (object) {
      var result = Meteor.http.post(
         "http://localhost:8080",
         { params: { command: "add_object", value: object} } );
  
  
     },
    changed: function (object) {
      oldValue = ???   -&gt; how can I get it?
       var result = Meteor.http.post(
      "http://localhost:8080",
          { params: {command:"modify_object",oldValue: oldValue,newValue: object}} );
  
  
         },
    removed: function (object) {
        var result = Meteor.http.post(
       "http://localhost:8080",
       { params: { command: "remove_object",value: object } } );
  
     }
  }); 
  </code></pre>
  
  <p>so my qustions are like this:</p>
  
  <ol>
  <li><p>how can I get all collections and observe changes on them?</p></li>
  <li><p>When object modified how can I get the old value?</p></li>
  </ol>