Test exception type on failure.

When we stop retrying, because of recurring exception
we expect the decorator to raise the last raised exception
without any wrapping (if wrap_exception==False)
cf #8
We test this behavior in a new unit test.
If possible, raise the last exception when stopping

When we stop retrying because of recurring exceptions,
we expect the decorator to raise the last exception.
(if wrap_exception==False)
This commit fixes issue #8.
Update AUTHORS.rst