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 don't get this - you are trying to create an entry based on a non-existent key, yet the implementation will actually never invoke the function with these keys. That's because you're computing mappings for keys {4, 5, 6}. The previous version had it right - it ignored the passed in keys, and returned a set that contained unrequested keys - these mappings should be ignored (incidentally, this test will fail due to the issue I pointed out in my other comment for `OnHeapStore` above).