Add a failing test and a naive synchronized implementation

- SyncedKeyResourcePool uses a normal Map with a var and uses synchronized to make sure things are ok
Make KeyedResourcePool rely on Symbols
Replace old implementation with new
Add a WIP test for cleanObsolete vs getOrCreate 'race condition'
RWLocks instead, allow any kind of key again
Merge pull request #68 from lloydmeta/feature/fix-keyed-pool-race

Fix/enhance KeyedResourcePool