title: ArgumentError in #new, Subclassing Enumerator
body: <p>I'm subclassing <code>Enumerator</code> like this:</p>
  
  <pre><code>class CuadraticPrimeGenerator &lt; Enumerator
    def initialize(a=1,b=49)
      super do |y|
        x = 1
        loop do 
          y &lt;&lt; x**2 + a*x + b
          x += 1
        end
      end
    end
  end
  </code></pre>
  
  <p>However...</p>
  
  <pre><code>&gt; CuadraticPrimeGenerator.new(1,49)
  0027.rb:41:in `initialize': 49 is not a symbol (TypeError)
      from 0027.rb:41:in `initialize'
      from 0027.rb:48:in `new'
      from 0027.rb:48:in `&lt;main&gt;'
  </code></pre>
  
  <p>Thoughts?</p>