NTFS: Support more clean journal ($LogFile) states.

      - Support journals ($LogFile) which have been modified by chkdsk.  This
        means users can boot into Windows after we marked the volume dirty.
        The Windows boot will run chkdsk and then reboot.  The user can then
        immediately boot into Linux rather than having to do a full Windows
        boot first before rebooting into Linux and we will recognize such a
        journal and empty it as it is clean by definition.
      - Support journals ($LogFile) with only one restart page as well as
        journals with two different restart pages.  We sanity check both and
        either use the only sane one or the more recent one of the two in the
        case that both are valid.

Signed-off-by: Anton Altaparmakov <aia21@cantab.net>