title: RestKit - Nested Structure Fail
body: <p>I am currently using RestKit in our project but I am facing some issues to manage this structure:</p>
  
  <pre><code>{"Elements": [
      {
        "Element": {
          "id": "1",
          "property": "house",
          "_addons": [
            {
              "Links": [
                {
                  "Link": {
                    "id": "2",
                    "url": "http://www.google.com"
                  }
                },
                {
                  "Link": {
                    "id": "3",
                    "url": "http://www.google.com"
                  }
                }
              ]
            }
          ]
        }
      },
      {
        "Element": {
          "id": "2",
          "property": "garage",
          "_addons": [
            {
              "Links": [
                {
                  "Link": {
                    "id": "4",
                    "url": "http://www.google.com"
                  }
                },
                {
                  "Link": {
                    "id": "5",
                    "url": "http://www.google.com"
                  }
                }
              ]
            }
          ]
        }
      }
    ]
  }
  </code></pre>
  
  <p>Right now in the object Element, there is the property "links"  which is a <code>NSMutableArray</code> (I tried also with `NSMutableDictionary but the problem is still there). Now, 
  if I try to do </p>
  
  <p><code>[mapping addPropertyMapping:[RKRelationshipMapping relationshipMappingFromKeyPath:@"_addons.Links.Link" toKeyPath:@"links" withMapping:[Link mapping]]];</code></p>
  
  <p>I receive an error saying that I wasn't possibile to map and there is a collection inside a collection. </p>
  
  <p>The only solution I found was to include <code>@"_addons.Links" : @"links"</code> in the mapping dictionary. In this case, though, I "lose" the chance to have the mapping to Link objects and I have to do it manually. Anybody has any advice?</p>