Display line numbers for failed assertions

Adds v3 tests to the PHPUNIT filter whitelist, so that the line number at which the test fails will be reported. (A more future-proof solution would be to move all test helper classes which are not themselves test classes to a subdirectory, and blacklist that dir only. That dir could be tests/phpunit/CiviTest, and I think the only helper class not already there is Utils.php, but maybe I am missing something.)