More test fixes, and maybe a fix to the flattener (let's see if there's any regression..)

core/API/DataTableManipulator/Flattener.php

plugins/AnonymousPiwikUsageMeasurement

...ystem/expected/test_Contents__Actions.getPageUrls_day.xml

...tem/expected/test_Contents__Actions.getPageUrls_month.xml

...xamplePlugin/tests/System/expected/test___API.get_day.xml

tests/PHPUnit/System/AutoSuggestAPITest.php

...te1_OldReportsShouldAppear__Actions.getPageUrls_month.xml

...te2_OldReportsShouldAppear__Actions.getPageUrls_month.xml

...Flat_rankingQueryDisabled__Actions.getDownloads_range.xml