Add ref counting to which leveldb shards are open so they can be closed after references released
Fix bug where I was deleting the shard reference before pulling out the shard to close it
Add test for max shards and fix bug in closing out old one
Updated ref counting to remove accessed shards from the list of ones to close. Updated the close to close as many as it takes to get below the leve
Merge pull request #301 from influxdb/ref-count-on-open-shards

Add ref counting to which leveldb shards are open so they can be closed ...