form of a some expressions when referring to the ``.c`` collection
on a ``select()`` construct, but the ``str()`` form isn't available
since the element relies on dialect-specific compilation constructs,
notably the ``__getitem__()`` operator as used with a Postgresql
``ARRAY`` element.  The fix also adds a new exception class
:class:`.UnsupportedCompilationError` which is raised in those cases
where a compiler is asked to compile something it doesn't know
how to.  Also in 0.8.3.
[ticket:2780]

:meth:`.Insert.from_select`.  Given a list of columns and
a selectable, renders ``INSERT INTO (table) (columns) SELECT ..``.
While this feature is highlighted as part of 0.9 it is also
backported to 0.8.3. [ticket:722]
- The :func:`.update`, :func:`.insert`, and :func:`.delete` constructs
will now interpret ORM entities as FROM clauses to be operated upon,
in the same way that select() already does.  Also in 0.8.3.

- add support for correlations to propagate all the way in; because
correlations require context now, need to make sure a select enclosure
of any level takes effect any number of levels deep.
- fix what we said correlate_except() was supposed to do when we first
released #2668 - "the FROM clause is left intact if the correlated SELECT
is not used in the context of an enclosing SELECT..." - it was not
considering the "existing_froms" collection at all, and prohibited
additional FROMs from being placed in an any() or has().
- add test for multilevel any()
- lots of docs, including glossary entries as we really need to define
"WHERE clause", "columns clause" etc. so that we can explain correlation better
- based on the insight that a SELECT can correlate anything that ultimately
came from an enclosing SELECT that links to this one via WHERE/columns/HAVING/ORDER BY,
have the compiler keep track of the FROM lists that correspond in this way,
link it to the asfrom flag, so that we send to _get_display_froms() the exact
list of candidate FROMs to correlate.  no longer need any asfrom logic in the
Select() itself
- preserve 0.8.1's behavior for correlation when no correlate options are given, not
to mention 0.7 and prior's behavior of not propagating implicit correlation more than one level..
this is to reduce surprises/hard-to-debug situations when a user isn't trying
to correlate anything.

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

- clean up inspect() calls within query._join()
- make sure join.alias(flat) propagates
- fix almost all assertion tests

might even be most of the tests we need (though dedicated sql tests would be needed anyway)