Pull request courtesy Stefan Urbanek.  fixes #1957

be properly typed as boolean in the result, and also would fail to be
anonymously aliased in a SELECT list as is the case with a
non-negated EXISTS construct.
fixes #3682

- establish consistent names between existing unconsumed names tests and new ones
added per ref #3666

for ref #3657.  The Oracle dialect makes more use of the "select_wraps_for"
feature than SQL server because Oracle doesn't have "TOP" for a limit-only
select, so tests are showing more happening here.  In the case where
the select() has some dupe columns, these are deduped from the .c collection
so a positional match between the wrapper and original can't use .inner_columns,
because these collections wont match.  Using _columns_plus_names
instead which is the deduped collection that determines the SELECT display,
which definitely have to match up.

(cherry picked from commit aa9ce3f521f254da9879ede011e520ec35b8270e)

handled within visit_select(); this attribute was added in the
1.0 series to accommodate the subquery wrapping behavior of
SQL Server and Oracle while also working with positional
column targeting and no longer relying upon "key fallback"
in order to target columns in such a statement.  The IBM DB2
third-party dialect also has this use case, but its implementation
is using regular expressions to rewrite the textual SELECT only
and does not make use of a "wrapped" select at this time.
The logic no longer attempts to reconcile proxy set collections as
this was not deterministic, and instead assumes that the select()
and the wrapper select() match their columns postionally,
at least for the column positions they have in common,
so it is now very simple and safe.  fixes #3657.
- as a side effect of #3657 it was also revealed that the
strategy of calling upon a ResultProxy._getter was not
correctly calling into NoSuchColumnError when an expected
column was not present, and instead returned None up to
loading.instances() to produce NoneType failures; added
a raiseerr argument to _getter() which is called when we
aren't expecting None, fixes #3658.

- move tests to CRUDTest
- changelog, fixes #3643

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

This supports the use case of an application that uses the same set of
:class:`.Table` objects in many schemas, such as schema-per-user.
A new execution option
:paramref:`.Connection.execution_options.schema_translate_map` is
added. fixes #2685
- latest tox doesn't like the {posargs} in the profile rerunner

such as a CHECK constraint would render an erroneous comma in the
definition; this scenario can occur such as with a Postgresql
INHERITS table that has no columns of its own.
fixes #3598