Resolve dependency cycle

I had the dependency cycle issue mention in #2 and #3. From the comments, I formed a quick fix which I turn into a full pull-request with this.

I digressed a little with removing deprecation warnings and cleaning up whitespace. I also extracted some common things in the specs which should clarify the different levels better.

Locally, everything is green (`rake spec`). The change itself (setting notify and require directly on Concat[/etc/exports]) is working, I took it from my live environment.

I hope that I didn't mess up things for Redhat-installations.