Vip restricted commands check fixes

Couple of simple fixes for VIPRestrictedCommands[Check|Test], required for the migration to PHP-Parser.
This is actually something I'm tackling with my php-parser-checks branch. For example, when calling `add_error()` in that branch, line numbers and filenames get added automatically by `PhpFileCheckVisitor`, upon which e.g. `FunctionCallCheckVisitor` is based (as could a prospective `ClassCheckVisitor`). I haven't converted this one check there yet, but here is what `ForbiddenFunctionsCheck` will look like: https://github.com/ockham/vip-scanner/blob/aa4015fc4a95c1879897195560f4b85ce958e06c/vip-scanner/checks/ForbiddenFunctionsCheck.php
This one could be similar.