rework CacheWriter writeAll() and deleteAll() to permit partial success

If you use the following, you can drop the "rawtypes" reference.  (I've not kept up with the workings of the Java implementation crew, but, at one point in time, the use of raw types was slated to be disallowed.)
```java
    successes.addAll((Collection<K>)bcwe.getSuccesses());
    failures.putAll((Map<K, Exception>)bcwe.getFailures());
```