when the construct contains non-standard sql elements such as
returning, array index operations, or dialect-specific or custom
datatypes.  a string is now returned in these cases rendering an
approximation of the construct (typically the postgresql-style
version of it) rather than raising an error. fixes #3631
- add within_group to top-level imports
- add eq_ignore_whitespace to sqlalchemy.testing imports

un-adjusted internal symbol names for "anonymous" labels, which
are the "foo_1" types of labels we see generated for SQL functions
without labels and similar.  This was a side effect of the
performance enhancements implemented as part of references #918.
fixes #3483

- fix TablesTest to use the bind that we've returned from setup_bind()
to emit DELETE statements

and ``__declare_last__`` accessors where these would no longer be
called on the superclass of the declarative base.
fixes #3383

sort_tables_and_constraints function.
- The DDL generation system of :meth:`.MetaData.create_all`
and :meth:`.Metadata.drop_all` has been enhanced to in most
cases automatically handle the case of mutually dependent
foreign key constraints; the need for the
:paramref:`.ForeignKeyConstraint.use_alter` flag is greatly
reduced.  The system also works for constraints which aren't given
a name up front; only in the case of DROP is a name required for
at least one of the constraints involved in the cycle.
fixes #3282

constructs are now importable from the "from sqlalchemy" namespace,
just like every other Core construct.
- The implicit conversion of strings to :func:`.text` constructs
when passed to most builder methods of :func:`.select` as
well as :class:`.Query` now emits a warning with just the
plain string sent.   The textual conversion still proceeds normally,
however.  The only method that accepts a string without a warning
are the "label reference" methods like order_by(), group_by();
these functions will now at compile time attempt to resolve a single
string argument to a column or label expression present in the
selectable; if none is located, the expression still renders, but
you get the warning again. The rationale here is that the implicit
conversion from string to text is more unexpected than not these days,
and it is better that the user send more direction to the Core / ORM
when passing a raw string as to what direction should be taken.
Core/ORM tutorials have been updated to go more in depth as to how text
is handled.
fixes #2992

N occurrences of a parameterized string.   This allows parameterized
warnings that can refer to their arguments to be delivered a fixed
number of times until allowing Python warning filters to squelch them,
and prevents memory from growing unbounded within Python's
warning registries.
fixes #3178

sqlalchemy/orm, sqlalchemy/event, sqlalchemy/testing

to get all flake8 passing