We've tried this recently with 1.8.2.0. You don't really need to create a module just to add a category attribute, once. It seems such a waste to go through so much file cruft to get something installed just once.
Category attributes tend to stay permanently once installed so what worked better for us is to just use a one-off script. Save this one right at magento root.
<?php
require_once "app/Mage.php";
Mage::app()->setCurrentStore(Mage::getModel('core/store')->load(Mage_Core_Model_App::ADMIN_STORE_ID));
$installer = new Mage_Sales_Model_Mysql4_Setup;
// change details below:
$attribute = array(
'type' => 'int',
'label'=> 'Your attribute label',
'input' => 'text',
'global' => Mage_Catalog_Model_Resource_Eav_Attribute::SCOPE_GLOBAL,
'visible' => true,
'required' => false,
'user_defined' => true,
'default' => "",
'group' => "General Information"
);
$installer->addAttribute('catalog_category', 'your_attribute_code', $attribute);
$installer->endSetup();
Save it as add_category_attribute.php
or something else memorable for you.
You can either use the browser to get to this file, or use php-cli
to run this:
php -f add_category_attribute.php
Good luck.