Description:
------------
---
From manual page: http://www.php.net/function.class-exists
---
bool class_exists ( string $class_name [, bool $autoload = true ] )

参数
class_name
   类名。名字的匹配是大小写不敏感的。(此处错误! 应该是区分大小写)



Test script:
---------------
namespace app\libs;

class Common
{
}

$class = 'app\\libs\\common';
var_dump(class_exists($class)); // 返回false
$class = 'app\\libs\\Common';
var_dump(class_exists($class)); // 返回true