checked out count if an existing pooled connection failed to reconnect
after an invalidate or recycle event.  Also in 0.8.3.
[ticket:2772]

make sure that the DBAPI connection passed to the reset-on-return events/dialect hooks
is also a "fairy", so that dictionaries like "info" are available.  [ticket:2770]
- rework the execution_options system so that the dialect is given the job of making
any immediate adjustments based on a set event.  move the "isolation level" logic to use
this new system.   Also work things out so that even engine-level execution options
can be used for things like isolation level; the dialect attaches a connect-event
handler in this case to handle the task.
- to support this new system as well as further extensibiltiy of execution options
add events engine_connect(), set_connection_execution_options(), set_engine_execution_options()

at the nose command line

actual mock objects from the mock library.  I'd like to use mock
for new tests so we might as well use it in obvious places.
- use unittest.mock in py3.3
- changelog
- add a note to README.unittests
- add tests_require in setup.py
- have tests import from sqlalchemy.testing.mock
- apply usage of mock to one of the event tests.  we can be using
this approach all over the place.