Fixed bug involving new value translation and validation feature
in :class:`.Enum` whereby using the enum object in a string
concatenation would maintain the :class:`.Enum` type as the type
of the expression overall, producing missing lookups.  A string
concatenation against an :class:`.Enum`-typed column now uses
:class:`.String` as the datatype of the expression itself.

Change-Id: Id402054e3ef008e0250c740dbb7e1c80f339fe78
Fixes: #3833

Ensure TypeDecorator delegates _set_parent_with_dispatch as well as
_set_parent to itself as well as its impl, as the TypeDecorator
class itself may have an active SchemaType implementation as well.

Fixed regression which occurred as a side effect of :ticket:`2919`,
which in the less typical case of a user-defined
:class:`.TypeDecorator` that was also itself an instance of
:class:`.SchemaType` (rather than the implementation being such)
would cause the column attachment events to be skipped for the
type itself.

Change-Id: I0afb498fd91ab7d948e4439e7323a89eafcce0bc
Fixes: #3832

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

The Boolean and Enum types both place SchemaType second in the
inheritance hierarchy.  In the case of Enum, this works
out that the copy() method is called from the base TypeEngine
which fails to transfer _create_events.   The test suite
doesn't seem to work with the inhertance hierarchy set up like
this as the event listeners don't work out, the _on_metadata_create
and _on_table_create hooks cause the production of an adapted type
which then adds event listeners that cause deque changed while
iteration.  It's not clear why Enum /Boolean don't have this problem.
But in any case it seems like the class mechanics for these types
remains fragile and would benefit from yet another refactor someday.

Change-Id: Ib641a5d2321b00f58bbe98dd0c5e789374db32b2
Fixes: #3827

Users are complaining that IntegrityError is no longer
raised.

Change-Id: I0855d5b7a98d4338f0910501b6e6d404ba33634d
Fixes: #3216

Compiler can now set up execution options and additionally
will propagate autocommit from embedded CTEs.

Change-Id: I19db7b8fe4d84549ea95342e8d2040189fed1bbe
Fixes: #3805

ORM attributes can now be assigned any object that is has a
``__clause_element__()`` attribute, which will result in inline
SQL the way any :class:`.ClauseElement` class does.  This covers other
mapped attributes not otherwise transformed by further expression
constructs.

As part of this, it was considered that we could add
__clause_element__() to ClauseElement, however this causes endless loops
in a "while" pattern and this pattern has been identified in third
party libraries.  Add a test to ensure we never make that change.

Change-Id: I9e15b3f1c4883fd3909acbf7dc81d034c6e3ce1d
Fixes: #3802

Added compiler-level flags used by Postgresql to place additional
parenthesis than would normally be generated by precedence rules
around operations involving JSON, HSTORE indexing operators as well as
within their operands since it has been observed that Postgresql's
precedence rules for at least the HSTORE indexing operator is not
consistent between 9.4 and 9.5.

Fixes: #3806
Change-Id: I5899677b330595264543b055abd54f3c76bfabf2