as :class:`.TypeDecorator` objects.

dialect on a type where MySQL does not support CAST; MySQL only
supports CAST on a subset of datatypes.   SQLAlchemy has for a long
time just omitted the CAST for unsupported types in the case of
MySQL.  While we don't want to change this now, we emit a warning
to show that it's taken place.   A warning is also emitted when
a CAST is used with an older MySQL version (< 4) that doesn't support
CAST at all, it's skipped in this case as well.
fixes #3237

commit of pr152

all cases, so that MySQL 5.6.6 with the
``explicit_defaults_for_timestamp`` flag enabled will
will allow TIMESTAMP to continue to work as expected when
``nullable=False``.  Existing applications are unaffected as
SQLAlchemy has always emitted NULL for a TIMESTAMP column that
is ``nullable=True``.  fixes #3155

the ARRAY type when using psycopg2.  The psycopg2 dialect now
employs use of the psycopg2.extras.register_uuid() hook
so that UUID values are always passed to/from the DBAPI as
UUID() objects.   The :paramref:`.UUID.as_uuid` flag is still
honored, except with psycopg2 we need to convert returned
UUID objects back into strings when this is disabled.
fixes #2940

using psycopg2 2.5.4 or greater, which features native conversion
of JSONB data so that SQLAlchemy's converters must be disabled;
additionally, the newly added psycopg2 extension
``extras.register_default_jsonb`` is used to establish a JSON
deserializer passed to the dialect via the ``json_deserializer``
argument.  Also repaired the Postgresql integration tests which
weren't actually round-tripping the JSONB type as opposed to the
JSON type.  Pull request courtesy Mateusz Susik.

- Repaired the use of the "array_oid" flag when registering the
HSTORE type with older psycopg2 versions < 2.4.3, which does not
support this flag, as well as use of the native json serializer
hook "register_default_json" with user-defined ``json_deserializer``
on psycopg2 versions < 2.5, which does not include native json.

consists mainly of adjusting fixtures to ensure connections are closed
explicitly.  psycopg2cffi also handles unicode bind parameter
names differently than psycopg2, and seems to possibly have a little less
control over floating point values at least in one test which is
marked as a "fail", though will see if it runs differently on linux
than osx..
- changelog for psycopg2cffi, fixes #3052