Use a slightly more recent version of mitsuba and fix locale

[jammm]

Did this to fix cpu affinity issue and some missing locale issue which occurred in a local cluster in my University's network.

[marceliwac]

I would hold off merging this just yet (see commit discussion for details) and wait until the tagged releases are supported on mitsuba-renderer/mitsuba. I've created an Issue to support tagged versioning on Mitsuba's official GitHub repo.