Complex test suite may out of memory
Following #357 and d03994b we have out-of-memory in some builds:

- Travis OOM: https://travis-ci.org/mratsim/Arraymancer/jobs/542973325#L1059
- Appveyor x64 success and x32 OOM: https://ci.appveyor.com/project/mratsim/arraymancer/builds/25131456