[USETUP] Improve the NTOS installations detector.

[USETUP] Improve the NTOS installations detector.

In all the disks/partitions available, it searches for the presence of freeldr.ini / boot.ini, open & parse them,
and enumerates the available boot entries (as candidates for installations). For each of them, it maps their ARC paths
into the NT namespace (hence the ARC 2 NT path resolver committed in r74621), then attempts to detect in these paths
the existence of NTOS installations.

svn path=/branches/setup_improvements/; revision=74622