Allow conditional checks for filesystem

[Former user]

Using % Values is cumbersome when dealing with large filesystems. In order to use the same check for all filesystem-sizes there should be a possibility to use conditional checks.

e.g. if space usage > 95% and space free < 5 GB then alert

[Tildeslash]

It won't make sense ... if you already know, that you want to be alerted only when less then 5GB is left, then use just:

if space free < 5 GB then alert