Change-Id: I4e8c2aa8fe817bb2af8707410fa0201f938781de

This allows to skip buffering of the results on the client side, e.g.
the following snippet:

    table = sa.Table(
        'testtbl', sa.MetaData(),
        sa.Column('id', sa.Integer, primary_key=True),
        sa.Column('a', sa.Integer),
        sa.Column('b', sa.String(512))
    )
    table.create(eng, checkfirst=True)

    with eng.connect() as conn:
        result = conn.execute(table.select().limit(1)).fetchone()
        if result is None:
            for _ in range(1000):
                conn.execute(
                    table.insert(),
                    [{'a': random.randint(1, 100000),
                      'b': ''.join(random.choice(string.ascii_letters) for _ in range(100))}
                      for _ in range(1000)]
                )

    with eng.connect() as conn:
        for row in conn.execution_options(stream_results=True).execute(table.select()):
            pass

now uses ~23 MB of memory instead of ~327 MB on CPython 3.5.2 and
PyMySQL 0.7.9.

psycopg2 implementation and execution options (stream_results,
server_side_cursors) are reused.

Change-Id: I4dc23ce3094f027bdff51b896b050361991c62e2

This is another psycopg2 error message representing an
unusable connection.

Fixes #3715
Change-Id: Ida6e212963e9c7336bf2944e7ef928619ac3a0e7
Pull-request: https://bitbucket.org/zzzeek/sqlalchemy/pull-requests/85

persistence of JSON values in MySQL as well as basic operator support
of "getitem" and "getpath", making use of the ``JSON_EXTRACT``
function in order to refer to individual paths in a JSON structure.
fixes #3547
- Added a new type to core :class:`.types.JSON`.  This is the
base of the PostgreSQL :class:`.postgresql.JSON` type as well as that
of the new :class:`.mysql.JSON` type, so that a PG/MySQL-agnostic
JSON column may be used.  The type features basic index and path
searching support.
fixes #3619
- reorganization of migration docs etc. to try to refer both to
the fixes to JSON that helps Postgresql while at the same time
indicating these are new features of the new base JSON type.
- a rework of the Array/Indexable system some more, moving things
that are specific to Array out of Indexable.
- new operators for JSON indexing added to core so that these can
be compiled by the PG and MySQL dialects individually
- rename sqltypes.Array to sqltypes.ARRAY - as there is no generic
Array implementation, this is an uppercase type for now, consistent
with the new sqltypes.JSON type that is also not a generic implementation.
There may need to be some convention change to handle the case of
datatypes that aren't generic, rely upon DB-native implementations,
but aren't necessarily all named the same thing.

- The "hashable" flag on special datatypes such as :class:`.postgresql.ARRAY`,
:class:`.postgresql.JSON` and :class:`.postgresql.HSTORE` is now
set to False, which allows these types to be fetchable in ORM
queries that include entities within the row.  fixes #3499
- The Postgresql :class:`.postgresql.ARRAY` type now supports multidimensional
indexed access, e.g. expressions such as ``somecol[5][6]`` without
any need for explicit casts or type coercions, provided
that the :paramref:`.postgresql.ARRAY.dimensions` parameter is set to the
desired number of dimensions. fixes #3487
- The return type for the :class:`.postgresql.JSON` and :class:`.postgresql.JSONB`
when using indexed access has been fixed to work like Postgresql itself,
and returns an expression that itself is of type :class:`.postgresql.JSON`
or :class:`.postgresql.JSONB`.  Previously, the accessor would return
:class:`.NullType` which disallowed subsequent JSON-like operators to be
used. part of fixes #3503
- The :class:`.postgresql.JSON`, :class:`.postgresql.JSONB` and
:class:`.postgresql.HSTORE` datatypes now allow full control over the
return type from an indexed textual access operation, either ``column[someindex].astext``
for a JSON type or ``column[someindex]`` for an HSTORE type,
via the :paramref:`.postgresql.JSON.astext_type` and
:paramref:`.postgresql.HSTORE.text_type` parameters. also part of fixes #3503
- The :attr:`.postgresql.JSON.Comparator.astext` modifier no longer
calls upon :meth:`.ColumnElement.cast` implicitly, as PG's JSON/JSONB
types allow cross-casting between each other as well.  Code that
makes use of :meth:`.ColumnElement.cast` on JSON indexed access,
e.g. ``col[someindex].cast(Integer)``, will need to be changed
to call :attr:`.postgresql.JSON.Comparator.astext` explicitly.  This is
part of the refactor in references #3503 for consistency in operator
use.

"max_row_buffer" execution option for BufferedRowResultProxy
- also add documentation, changelog and version notes
- rework the max_row_buffer argument to be interpreted from
the execution options upfront when the BufferedRowResultProxy
is first initialized.

psycopg2cffi dialect, in particular that the current 2.7.0 version
does not have native support for the JSONB type.  The version detection
for psycopg2 features has been tuned into a specific sub-version
for psycopg2cffi.  Additionally, test coverage has been enabled
for the full series of psycopg2 features under psycopg2cffi.
fixes #3439

:func:`.engine_from_config` were not being parsed correctly;
these included ``pool_threadlocal`` and the psycopg2 argument
``use_native_unicode``. fixes #3435
- add legacy_schema_aliasing config parsing for mssql
- move use_native_unicode config arg to the psycopg2 dialect