Option to set and activate the DELDIR env var is missing

[Lutz R. Pescht]

While FM/2 uses the DELDIR statement if set an option to activate and adjust this is missing. A page in the settings notebook could be added to allow this being set per drive (directory and size limit) as well as indicating current usage of this space. The info dialog for drives should also show this detail and allow for changes. I'm still using DELDIR as it works on LAN shares while Trashcan does not.