Dictionary import tests and Temporary file test util

I can see why this is like this (I assume to make it feasible to clean-up resources). @etorreborre @charleso @nhibberd do any of you see a way in which we could get the property (or write new version of prop) to do the cleanup automatically, i.e. `propIO((r: TempoaryRepository, r: TemporaryReferenceFile) => ...)`. This would be nice, but I can't see a really feasible (not horribly buggy) way to do it.