target :class:`.Column` has been reworked to be as
immediate as possible, based on the moment that the
target :class:`.Column` is associated with the same
:class:`.MetaData` as this :class:`.ForeignKey`, rather
than waiting for the first time a join is constructed,
or similar. This along with other improvements allows
earlier detection of some foreign key configuration
issues.  Also included here is a rework of the
type-propagation system, so that
it should be reliable now to set the type as ``None``
on any :class:`.Column` that refers to another via
:class:`.ForeignKey` - the type will be copied from the
target column as soon as that other column is associated,
and now works for composite foreign keys as well.
[ticket:1765]

called :attr:`.TypeDecorator.coerce_to_is_types`,
to make it easier to control how comparisons using
``==`` or ``!=`` to ``None`` and boolean types goes
about producing an ``IS`` expression, or a plain
equality expression with a bound parameter.
[ticket:2744]

- docs docs docs

Conflicts:
	test/profiles.txt
	test/sql/test_selectable.py

- fix the result map rewriter for col mismatches, since the rewritten
select at the moment typically has more columns than the original

the joins as is, regardless of the dialect not supporting it.  use_labels=True
indicates a higher level of automation and also can maintain the labels
between rewritten and not.  use_labels=False indicates a manual use case.