This allows automap to reflect tables from a schema other than the
default without the need to resort to calling MetaData.reflect
directly.

Change-Id: Ie73cb113bd6d115555c09c5efc33d27ad2c9c512
Pull-request: https://github.com/zzzeek/sqlalchemy/pull/237

``cascade="all, delete-orphan"`` automatically on a one-to-many
relationship/backref where the foreign key is detected as containing
one or more non-nullable columns.  This argument is present in the
keywords passed to :func:`.automap.generate_relationship` in this
case and can still be overridden.  Additionally, if the
:class:`.ForeignKeyConstraint` specifies ``ondelete="CASCADE"``
for a non-nullable or ``ondelete="SET NULL"`` for a nullable set
of columns, the argument ``passive_deletes=True`` is also added to the
relationship.  Note that not all backends support reflection of
ondelete, but backends that do include Postgresql and MySQL.
fixes #3210

Removed ungrammatical apostrophes from documentation, replacing
"it's" with "its" where appropriate (but in a few cases with "it is"
when that read better).

While doing that, I also fixed a couple of minor typos etc.
as I noticed them.

not be created between two classes that are in a joined inheritance
relationship, for those foreign keys that link the subclass back to
the superclass.
fixes #3004

new automap extension would fail if classes
were pre-arranged in single or potentially joined inheritance patterns.
The repaired joined inheritance issue could also potentially apply when
using :class:`.DeferredReflection` as well.