Remove error suppression @ from the code

[obuisard]

We should not use @ in the code but rather make sure errors are reported.

For instance, in admin/tmpl/check/default.php:
if (@$data['databasemigratestatus'] == '0')
should be replaced with something like
if (isset($data['databasemigratestatus']) && $data['databasemigratestatus'] == '0')