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
The mapping function is actually free to return an empty `Iterable` here - this is in the javadoc. If it does, we need to simply return `oldValue` from here to retain the original mapping.