CachingStore: setUserAlertManager set the property in the *underlying* store
CachingFreenetStore: now pushAll return the number of bytes that it pushed down to the *underlying* store
CachingFreenetStoreTracker: fix in pushAllCachingStores and unregisterCachingFS, improvements and fixing in add
CachingFreenetStoreTest: add one check in testOnCloseSSK and testTimeExpireSSK and waiting the flushing of the cache in testOverMaximumSize