Issue 110 : bulkOperations integration tests

Several things to review here :
* the integration tests of course
* some rewrites of the putAll and removeAll methods (with some refactorings too)
Thanks for your input in advance
I'm not sure I'm fond of this way of testing write-through semantics. Perhaps you could mock both `CacheWriterFactory` and `CacheWriter` to explicitly modify a target map on `writeAll()` and `deleteAll()` - at least for readability's sake? Then you can also get rid of that ugly `throwsException` flag, and make your mock do one thing or another, depending on the test case.