QtIFW

Rewrite function to use QFile::map().

Once the data is mapped into memory, searching backwards is way faster.

Change-Id: I31667095712cfba95a8255e04d217ed9242fd2a8
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>
Reviewed-by: Tim Jenssen <tim.jenssen@digia.com>