Installation problems often come down to a 'white screen of death' either during installation or after it. The WSOD is generally caused by a PHP error that isn't picked up by SilverStripe's error handler. This change fixes the first of those.
As a bigger fix, I'd like to see us allow the installation of sites in dev mode, the enabling of display_errors=on in dev mode, and perhaps even the ability to easily perform an initial installation in dev mode before switching to live mode. However, that's a bigger change for another time.
2598f6596d