clear the store before state transfer

Right now, before integrating state (fetch persistent state = true) the cacheStore.clear() is performed within cacheStore. This cacheStore.clear() should be moved outside the store, in StateTransferManager, and state transfer should document that the the store is cleared before integrating remote state.
This is in relation to: http://lists.jboss.org/pipermail/infinispan-dev/2010-March/002483.html