Extend error handling via php shutdown function

The custom php error handler cannot capture errors of type E_ERROR, E_CORE_ERROR ... However, php shutdown function is called in case of these types (excluding E_PARSE of course). This makes it the place to log these errors in watchdog.

For D7 there is a project http://drupal.org/project/past which already utilises the shutdown function - you can get some overview about the errors and how they are handled via past here: http://techblog.md-systems.ch/tutorial-howto/2013-06-advanced-php-error-...