Fix interrupt handling during CacheStore.purge(...)

During cache shutdown, any persistence threads are interrupted. Some cache stores, e.g. JdbcBinaryStore, inappropriately rethrow InterruptedExceptions as PersistenceExceptions, which then get logged as ERROR by the ExpirationManager.
Other cache stores, e.g. SingleFileStore, don't handle/react to interrupts at all!
I haven't looked at every cache store implementation, but the problem seems widespread.