Fixing issue 45

Added some tests for #46. [Like AndreasPizsa](https://github.com/trek/grunt-neuter/pull/46#issuecomment-44628055), I also ran into difficulties writing these tests. I took some inspiration [straight from grunt-contrib-nodeunit](https://github.com/gruntjs/grunt-contrib-nodeunit/blob/master/test/nodeunit_test.js).

Note that the tests all failed on Windows, which is where [this](https://github.com/joeyespo/grunt-neuter/commit/7514ce10b26ec65c6d07ea443886f67095c720ac) came from so I could verify it all worked. That commit should only affect Windows users.