change default signature of `DataUtil::formatForOS()` to assume `$absolu...

...te=true`

revert 0fb40888377592d6301ba5a293d6029887bf4eea and revert 6dc17d928a27759e74f903c693cdd7b4c46e6ee4

refs zikula/core#782 and refs zikula/core#786