- The ``alembic revision`` command accepts the ``--sql`` option to
suit some very obscure use case where the ``revision_environment``
flag is set up, so that ``env.py`` is run when ``alembic revision``
is run even though autogenerate isn't specified.   As this flag is
otherwise confusing, error messages are now raised if
``alembic revision`` is invoked with both ``--sql`` and
``--autogenerate`` or with ``--sql`` without
``revision_environment`` being set.
fixes #248