title: Typed, nested map of map[string]interface{} returns "type interface {} does not support indexing"
body: <p>I'm experiencing a very strange problem with typed nested maps.</p>
  
  <pre><code>gore version 0.2.6  :help for help
  gore&gt; type M map[string]interface{}
  gore&gt; m := M{"d": M{}}
  main.M{"d":main.M{}}
  gore&gt; m["d"]["test"] = "will fail"
  # command-line-arguments
  /tmp/288178778/gore_session.go:13:8: invalid operation: m["d"]["test"] (type interface {} does not support indexing)
  /tmp/288178778/gore_session.go:14:17: invalid operation: m["d"]["test"] (type interface {} does not support indexing)
  error: exit status 2
  exit status 2
  gore&gt; m["e"] = "this works"
  "this works"
  gore&gt; m
  main.M{"d":main.M{}, "e":"this works"}
  </code></pre>
  
  <p>What am I doing wrong? Why does this suddenly fail just because the map is nested inside a map?</p>