dev/core#3979 - Add test to reproduce error

dev/core#3979 - Add test to reproduce error

Note: On current D7, this doesn't actually reproduce the message because `bootstrap.inc` redirects it

```
function _drupal_bootstrap_configuration() {
  // Set the Drupal custom error handler.
  set_error_handler('_drupal_error_handler');
  set_exception_handler('_drupal_exception_handler');
```

But if you comment out `set_error_handler()`, then it does. And I presume it would on D8+...