Allow Zen to be used on update.php and install.php pages

Trying to set my custom theme for install and update pages on drupal version 6.20 I had to do some changes. I write the code, hoping they may come in handy.

I have create a replacement function for variable_get, variable_set, and variable_del. (this function made access to db but is not initialized) and then i have substitute al call with the replaced function
zen_variable_get, Zen_variable_set, and zen_variable_del in all zen-internals files.

template.php

/**
 * Replace variable_get
 */
function zen_variable_get($name, $default) {
	return variable_get($name, $default);
}

/**
 * Replace variable_set
 */
function zen_variable_set($name, $value) {
	global $conf;
	if (defined('MAINTENANCE_MODE') && (MAINTENANCE_MODE == 'install' || MAINTENANCE_MODE == 'update')) {
		$conf[$name] = $value;
		return;
	}
	
	variable_set($name, $value);
}

/**
 * Replace variable_del
 */
function zen_variable_del($name) {
  global $conf;
  if (defined('MAINTENANCE_MODE') && (MAINTENANCE_MODE == 'install' || MAINTENANCE_MODE == 'update')) {
		$conf[$name] = $value;
		cache_clear_all('variables', 'cache');
		unset($conf[$name]);
		return;
  }  
  
  variable_del($name);
}

Then i have generate my custom maintenance-page.tpl.php and i have modify drupal core in file includes/theme.maintenance.inc

in function _drupal_maintenance_theme() at line 37

function _drupal_maintenance_theme() {
  global $theme, $theme_key;

  ....

  // Install and update pages are treated differently to prevent theming overrides.
  if (defined('MAINTENANCE_MODE') && (MAINTENANCE_MODE == 'install' || MAINTENANCE_MODE == 'update')) {
    //$theme = 'minnelli';
    $theme = 'zen';  //my custom theme
  }

  ...

in function theme_install_page () at line 116

function theme_install_page($content) {
  ....
  global $theme_path;

  //$theme_path = 'themes/garland';
  //return theme_render_template('themes/garland/maintenance-page.tpl.php', $variables);
  $theme_path = 'sites/all/themes/zen';  //@WORKAROUND update theme replacement
  return theme_render_template($theme_path . '/templates/maintenance-page.tpl.php', $variables);  
}

and the same to function theme_update_page () at line 170

function theme_update_page($content) {
  ....
  global $theme_path;

  //$theme_path = 'themes/garland';
  //return theme_render_template('themes/garland/maintenance-page.tpl.php', $variables);
  $theme_path = 'sites/all/themes/zen';  //@WORKAROUND update theme replacement
  return theme_render_template($theme_path . '/templates/maintenance-page.tpl.php', $variables);  
}

Sorry for my pour english.. =)