- Fixed bug which would occur if a DBAPI exception
occurs when the engine first connects and does its initial checks,
and the exception is not a disconnect exception, yet the cursor
raises an error when we try to close it.  In this case the real
exception would be quashed as we tried to log the cursor close
exception via the connection pool and failed, as we were trying
to access the pool's logger in a way that is inappropriate
in this very specific scenario. fixes #3063

Found using: https://github.com/intgr/topy

recycles the connection pool when a "disconnect" condition is detected;
instead of discarding the pool and explicitly closing out connections,
the pool is retained and a "generational" timestamp is updated to
reflect the current time, thereby causing all existing connections
to be recycled when they are next checked out.   This greatly simplifies
the recycle process, removes the need for "waking up" connect attempts
waiting on the old pool and eliminates the race condition that many
immediately-discarded "pool" objects could be created during the
recycle operation. fixes #2985

- remove informix, maxdb, access symbols from tests etc.

is recreated, due to a disconnect error.   This fixes a particular
issue in the Oracle 8 dialect, but in general the dialect.initialize()
phase should only be once per dialect.  Also in 0.8.3. [ticket:2776]

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.

so just unconditionally turn this into a list
- this one test segfaults only on py3k + cx_oracle