title: Backbone Validate does not work
body: <p>I am using Backbone's <code>validate</code> function to guarantee <code>Man</code> to have an <code>age</code> property more than 18. Here is my code:</p>
  
  <pre><code>var Man = Backbone.Model.extend({
      initialize : function(){
          this.on("error",function(model,error){
              alert(error);
          });
      },
      validate : function(attrs,options){
          if (attrs.age &lt; 18){
              return 'below 18';
          } 
      }
  })
  
  var man = new Man({name : 'qian', age : 12});
  </code></pre>
  
  <p>But looking at the result it seems that <code>validate</code> doesn't work.</p>