Changed the naming convention used when generating bound parameters
for a multi-VALUES insert statement, so that the numbered parameter
names don't conflict with the anonymized parameters of a WHERE clause,
as is now common in a PostgreSQL ON CONFLICT construct.

Change-Id: I3188d100fe4d322a47d344d6a63d3e40b915f228
Fixes: #3828

Users are complaining that IntegrityError is no longer
raised.

Change-Id: I0855d5b7a98d4338f0910501b6e6d404ba33634d
Fixes: #3216

Fixed bug in new CTE feature for update/insert/delete stated
as a CTE inside of an enclosing statement (typically SELECT) whereby
oninsert and onupdate values weren't called upon for the embedded
statement.

This is accomplished by consulting prefetch
for all statements.  The collection is also broken into
separate insert/update collections so that we don't need to
consult toplevel self.isinsert to determine if the prefetch
is for an insert or an update.  What we don't yet test for
are CTE combinations that have both insert/update in one
statement, though these should now work in theory provided
the underlying database supports such a statement.

Change-Id: I3b6a860e22c86743c91c56a7ec751ff706f66f64
Fixes: #3745

INSERT, UPDATE, and DELETE statements to both specify their own
WITH clause, as well as for these statements themselves to be
CTE expressions when they include a RETURNING clause.
fixes #2551

insert-default holding columns not otherwise included in the SET
clause (such as primary key cols) to get rendered into the RETURNING
even though this is an UPDATE.

- Major fixes to the :paramref:`.Mapper.eager_defaults` flag, this
flag would not be honored correctly in the case that multiple
UPDATE statements were to be emitted, either as part of a flush
or a bulk update operation.  Additionally, RETURNING
would be emitted unnecessarily within update statements.

fixes #3609

the :class:`.Select` construct would have its ``._raw_columns``
collection mutated in-place when compiling the :class:`.Insert`
construct, when the target :class:`.Table` has Python-side defaults.
The :class:`.Select` construct would compile standalone with the
erroneous column present subsequent to compilation of the
:class:`.Insert`, and the the :class:`.Insert` statement itself would
fail on a second compile attempt due to duplicate bound parameters.
fixes #3603

statement.  This feature is available by passing the
:paramref:`~.sqlalchemy.sql.expression.update.preserve_parameter_order`
flag either to the core :class:`.Update` construct or alternatively
adding it to the :paramref:`.Query.update.update_args` dictionary at
the ORM-level, also passing the parameters themselves as a list of 2-tuples.
Thanks to Gorka Eguileor for implementation and tests.
adapted from pullreq github:200