Type and provider unit specs

Add unit-level specs for mvn provider and type.

I'm looking at doing some work to add stale snapshot detection to the mvn provider and was thinking it'd be awfully nice to have some specs.  These are not (strictly speaking) TDD specs, but in many cases I:

1. Authored green specs based on existing code
2. Modified the code to go red and prove the specs are doing their job
3. Revert code modifications and get back to green

This was not done in all cases, but I'm reasonably certain the specs provide value most of the time.

Also, just in case you prefer your specs extra-WET I didn't squash the DRY commit.