Fixed bug where the "simple many-to-one" condition that allows  lazy
loading to use get() from identity map would fail to be  invoked if the
primaryjoin of the relationship had multiple clauses separated by AND
which were not in the same order as that of the primary key columns
being compared in each clause. This ordering
difference occurs for a composite foreign key where the table-bound
columns on the referencing side were not in the same order in the .c
collection as the primary key columns on the referenced side....which
in turn occurs a lot if one is using declarative mixins and/or
declared_attr to set up columns.

Change-Id: I66cce74f614c04ed693dc0d58ac8c952b2f8ae54
Fixes: #3788

Stringify of expression with unnamed :class:`.Column` objects, as
occurs in lots of situations including ORM error reporting,
will now render the name in string context as "<name unknown>"
rather than raising a compile error.

Change-Id: I76f637c5eb4cfdb1b526964cb001565b97e296da
Fixes: #3789

Raise a more descriptive exception / message when ClauseElement
or non-SQLAlchemy objects that are not "executable" are erroneously
passed to ``.execute()``; a new exception ObjectNotExecutableError
is raised consistently in all cases.

Change-Id: I2dd393121e2c7e5b6b9e40286a2f25670876e8e4
Fixes: #3786

Two @validates decorators that make use of the same name
is not supported.  Raise an exception.

Change-Id: Ia3e89ffdc9ef345a0de258e2ac0ac5e0bd421c61
Fixes: #3776

The approach here is still error prone
and hard to follow.  Reorganize the whole
thing to take a pretty blunt approach to
the structure of to_join().  Also fix some never-called
code (!) in _prep_for_joins() and ensure we re-use
an aliased object.

Fixes: #3774
Change-Id: Ie6319415ae7213b4a33eac2ab70803ad2880d340