IPRT: Separated out RTPathAbs from the posix, fixing it up for windows + OS/2, and made it generic. Also added some NT path routines.

SUPR3: Use NtDeviceIoControlFile instead of DeviceIoControl to avoid wasting precious ticks on silly API conversions.

IPRT: Wrote native NT directory enumeration - not enabled by default. Provides ChangeTime and later file ID (inode no). Can also enumerate object directories, just for the fun of it.

Rewrote fs-win.cpp into a pure native NT version, this fixes the symbolic-link-in-path-not-followed issues that caused by having to guess the volume root in order to make the win32 (wrapper) API happy.