Enhanced enhanced version

I added the magic threshold adaption from check_mk for large disks to the script.
https://github.com/pashol/nagios-checks/blob/master/check_win_snmp_disk.pl

Documentation for the magic number:
https://mathias-kettner.de/checkmk_filesystems.html
(Chapter df magic number)

I also eliminated the rounding of percentages. For large disks with a narrow warning/critical levels it could potentially cause problems.