This was causing issues with Alembic (https://bitbucket.org/zzzeek/alembic/issue/127/auto-generate-seems-to-miss-unsigned)

Conflicts:
	lib/sqlalchemy/orm/mapper.py

of dbapi.Error (such as ``TypeError``, ``NotImplementedError``, etc.)
will propagate the exception unchanged.  Previously,
the error handling specific to the ``connect()`` routine would both
inappropriately run the exception through the dialect's
:meth:`.Dialect.is_disconnect` routine as well as wrap it in
a :class:`sqlalchemy.exc.DBAPIError`.  It is now propagated unchanged
in the same way as occurs within the execute process. [ticket:2881]
- add tests for this in test_parseconnect, but also add tests in test_execute
to ensure the execute() behavior as well

attempts when an existing connection attempt is blocking.  Previously,
the production of new connections was serialized within the block
that monitored overflow; the overflow counter is now altered within
it's own critical section outside of the connection process itself.
[ticket:2880]

connection to be available, such that for a connection pool
with no timeout specified, it will every half a second break out of
the wait to check for the so-called "abort" flag, which allows the
waiter to break out in case the whole connection pool was dumped;
normally the waiter should break out due to a notify_all() but it's
possible this notify_all() is missed in very slim cases.
This is an extension of logic first introduced in 0.8.0, and the
issue has only been observed occasionally in stress tests.

requirements etc., just like 0.9