"history" on a relationship-bound attribute will now no longer emit
any SQL if the relationship is unloaded.

to support dialect-level reflection options for all :class:`.Table`
objects reflected.

- Added a new dialect-level argument ``postgresql_ignore_search_path``;
this argument is accepted by both the :class:`.Table` constructor
as well as by the :meth:`.MetaData.reflect` method.  When in use
against Postgresql, a foreign-key referenced table which specifies
a remote schema name will retain that schema name even if the name
is present in the ``search_path``; the default behavior since 0.7.3
has been that schemas present in ``search_path`` would not be copied
to reflected :class:`.ForeignKey` objects.  The documentation has been
updated to describe in detail the behavior of the ``pg_get_constraintdef()``
function and how the ``postgresql_ignore_search_path`` feature essentially
determines if we will honor the schema qualification reported by
this function or not. [ticket:2922]

- with select_from(), add external order by so that Oracle orders correctly

the schema target of a :class:`.ForeignKey` will not be changed unless
that schema matches that of the parent table.  That is, if
a table "schema_a.user" has a foreign key to "schema_b.order.id",
the "schema_b" target will be maintained whether or not the
"schema" argument is passed to :meth:`.Table.tometadata`.  However
if a table "schema_a.user" refers to "schema_a.order.id", the presence
of "schema_a" will be updated on both the parent and referred tables.
This is a behavioral change hence isn't likely to be backported to
0.8; it is assumed that the previous behavior is pretty buggy
however and that it's unlikely anyone was relying upon it.

Additionally, a new parameter has been added
:paramref:`.Table.tometadata.referred_schema_fn`.  This refers to a
callable function which will be used to determine the new referred
schema for any :class:`.ForeignKeyConstraint` encountered in the
tometadata operation.  This callable can be used to revert to the
previous behavior or to customize how referred schemas are treated
on a per-constraint basis.  [ticket:2913]

- rework the tests in test.sql.test_metadata, all the "tometadata" tests
now under new class ToMetaDataTest

oriented row lookups were not matching up to the ad-hoc :class:`.ColumnClause`
objects that :class:`.TextAsFrom` generates, thereby making it not
usable as a target in :meth:`.Query.from_statement`.  Also fixed
:meth:`.Query.from_statement` mechanics to not mistake a :class:`.TextAsFrom`
for a :class:`.Select` construct.  This bug is also an 0.9 regression
as the :meth:`.Text.columns` method is called to accommodate the
:paramref:`.text.typemap` argument. [ticket:2932]