Added some unit tests to see if we can find a memory leak around esent PersistantDictionary. But this seems OK...

Also added some unit tests around the EsentPersistentDictionary class.
Added in the PersitantDictionary method for cleaning up after itself and forced a GC cleanup in the Dispose method of the EsentPersistentDictionary.
Removed the Tests which create and disposes of 2048 EsentPersistentDictionary's as its an intergration test not a unit test and we dont want this running all the time, its very slow.