missing extension causes fatal error on manage extensions page

If one of the installed extensions is not in the extensions directory and you move a site, for example, you get a fatal error about the extension being missing. There is no way to deal with this through the UI & you need to hack it out of the database

C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Error.php, backtrace, 298
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Extensions\Extension.php, fatal, 168
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Extensions\Extension.php, _parseXMLFile, 120
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Extensions.php, readXMLInfo, 324
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Extensions.php, _discoverInstalled, 263
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Admin\Page\Extensions.php, getExtensions, 62
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Admin\Page\Extensions.php, preProcess, 132
C:\utils\eclipseworkspace\civicrm-4.2\CRM\Core\Invoke.php, run, 228
C:\utils\eclipseworkspace\civicrm-4.2\drupal\civicrm.module, invoke, 381
, civicrm_invoke,
C:\webroot\drupal\drupal-6.19\includes\menu.inc, call_user_func_array, 350
C:\webroot\drupal\drupal-6.19\index.php, menu_execute_active_handler, 17

Manage Extensions
Sorry but we are not able to provide this at the moment.
Extension file c:/webroot/sites/circus/files/civicrm/civicrm_extensions\nz.co.fuzion.paystation\info.xml does not exist.