Small test trifles/formatting fixed
Fix Atomic file generation when steps are run in parallel

We need to make sure that we don't create the tempdir for the pre_commit file
until we are in the child process. As long as the _tempdir attribute is lazy,
this should just work if the attribute isn't called outside the run() method.
Merge pull request #12 from maxmind/dave/atomic-fork-bug

Fix tempdir for Atomic steps disappearing before run() is called