Implemented platform testing in pymultinest demo

Addresses issue 13 (https://github.com/JohannesBuchner/PyMultiNest/issues/13) where Johannes suggested the fix but I think never implemented it.
Merge pull request #23 from keflavich/patch-1

Implemented platform probing in pymultinest demo -- by Adam Ginsburg
https://github.com/JohannesBuchner/PyMultiNest/issues/13