fix incorrect use of environment variables
fix incorrect use of np.append (which returns a new array rather than modifying the given array). This bug resulted in Result.col_times and Result.col_which to be incorrectly set to empty arrays
added unit test for catching problems with Result.col_times and Result.col_which
added missing import of assert_
Merge pull request #202 from jrjohansson/fix-mcsolve-issues

Fix mcsolve issues