Remove the index.php from admin URLs in Magento

OpenMage_Base_Model_Core_Store.php

<?php

class OpenMage_Base_Model_Core_Store extends Mage_Core_Model_Store
{
    /**
     * Add script file name to the URL if server rewrites are disabled or Magento is not installed
     *
     * NB: This differs from the parent just by not adding the script name to the URL for the admin site
     *
     * @param   string $url
     *
     * @return  string
     */
    protected function _updatePathUseRewrites($url)
    {
        if (!$this->getConfig(self::XML_PATH_USE_REWRITES) || !Mage::isInstalled()) {
            $indexFileName = $this->_isCustomEntryPoint() ? 'index.php' : basename($_SERVER['SCRIPT_FILENAME']);
            $url .= $indexFileName . '/';
        }

        return $url;
    }
}