Prefer /var/tmp over /tmp for large temporary files

Submitted by Richard

Assigned to Xfburn Bug Triage

Link to original bug (#12330)

Description

On many newer systems /tmp is a tmpfs not real storage and has limited space (Fedora defaults to 4GB).

There's probably several options to work around this but a couple are:

1. Test if /var/tmp exists and use it if it does.
2. Test if /tmp is tmpfs and use somewhere else if it is.