title: "Ambiguous use of 'propertyName'" error given overridden property with didSet observer
body: <p>I've got a simple scenario in which I have a parent class, Person, which defines a property called "name" and includes a "didSet" observer...</p>
  
  <pre><code>class Person {
  
      var name: String? {
      didSet {
          println("Person name was set.")
      }
      }
  
      init() {}
  }
  </code></pre>
  
  <p>I also have a subclass of Person called Employee which adds its own "didSet" observer for the "name" property so that it can monitor changes to that property...</p>
  
  <pre><code>class Employee: Person {
  
      override var name: String? {
      didSet {
          println("Employee name was set.")
      }
      }
  
  }
  </code></pre>
  
  <p>When I try to exercise the code I get compile error but I can't figure out why or how to fix it. Here's the code that exercises these classes...</p>
  
  <pre><code>var person = Person()
  person.name = "Bob"
  
  var employee = Employee()
  employee.name = "Sally"  // results in "Ambiguous use of 'name'" compile error
  </code></pre>