Provide unit test for upscale_perm

Based on the discussion in the thread http://www.opm-project.org/pipermail/opm/2013-April/000179.html, I have come up with a unit test for upscale_perm. This test:

* Execute binary `upscale_perm` with a call to routine `system()` provided by stdlib.h and store results in a temporary result file inside directory tests/
* Compare solution with a reference solution within a given relative tolerance