Issue #728702 by Crell, daffie, pillarsdotnet, pjcdawkins, Damien Tournoud,...

Issue #728702 by Crell, daffie, pillarsdotnet, pjcdawkins, Damien Tournoud, David_Rothstein, reglogge, amateescu, tim.plunkett, tstoeckler, xjm, hussainweb, alexpott, cweagans, Tor Arne Thune, catch: Visiting index.php should redirect to install.php if settings.php already has database credentials but database is empty