title: Fetch value of selection field instead of key
body: <p>I defined a <code>selection</code> field in one model.</p>
  
  <pre><code>type = fields.Selection([('a','A'),('b','B'),('c','C')])
  </code></pre>
  
  <p>In one of function i tried to get <code>string value</code> instead of <code>key</code>.</p>
  
  <pre><code>@api.multi
      def testFunc(self):
      for res in self:
          print'Value',res.type //It prints 'a'.
  </code></pre>
  
  <p>I need to print 'A'.</p>
  
  <p>How can i do this?</p>