title: Symbol to string issue
body: <p>Following code fails</p>
  
  <pre><code>world = :world
  result = 'hello' + world
  puts result #=&gt; can't convert Symbol into String
  </code></pre>
  
  <p>Following code works</p>
  
  <pre><code>world = :world
  result = "hello #{world}"
  puts result #=&gt; hello world
  </code></pre>
  
  <p>Why?</p>
  
  <p>Using ruby 1.8.7</p>