Changing how pathing is determined:
* Adding new property to riak_core.app.src called platform_data_dir
* Removed ring_state_dir from riak_core.app.src
* Adding function to riak_core_ring_manager named ring_dir() to build a path for the ring file using either platform_data_dir or ring_state_dir
Changing path to prevent double ring directories.
Adding the ring dir to platform_data_dir
Merge pull request #468 from bbrietzke/from-pr-464

Changing how pathing is determined