Per zendframework#55 (and originally reported as zendframework/zend-hydrator#19),
this patch does the following:

- Adds tests against the hydrate and extract methods to ensure that the
  event triggered is the zend-stdlib variant (as well as kept the tests
  for the zend-hydrator variants).
- Updated test expectations to check for `triggerEvent()` (and not
  `trigger()`), as the 1.1 version of zend-hydrator is now
  forwards-compatible with zend-eventmanager v3. This also required
  raising the minimum version of zend-hydrator to 1.1 so that tests do
  not need to be varied.
- Fixes the test assumptions in `testAdd()`, as attachment of the
  aggregate listener now calls the `attach()` method of the listener
  class, changing how the mock EM instance is called.

Close #56
Fixes #55
Fixes zendframework/zend-hydrator#19