has been liberalized to warn for values that aren't even string
values, such as integers; previously, the updated warning system
of 1.0 made use of string formatting operations which
would raise an internal TypeError.   While these cases should ideally
raise totally, some backends like SQLite and MySQL do accept them
and are potentially in use by legacy code, not to mention that they
will always pass through if unicode conversion is turned off
for the target backend.
fixes #3346

basically by caching them.
- improve LRUCache so that size management only proceeds
in one thread, add a real get() method

logic to some degree in DefaultExecutionContext.  In particular
we are removing post_insert() which doesn't appear to be used
based on a survey of prominent third party dialects.  Callcounts
aren't added to existing execute profiling tests and inserts might be
a little better.
- simplify the execution_options join in DEC.  Callcounts don't
appear affected.

now be constructed such that the visit methods receive an indication
of the owning expression object, if any.  Any visit method that
accepts keyword arguments (e.g. ``**kw``) will in most cases
receive a keyword argument ``type_expression``, referring to the
expression object that the type is contained within.  For columns
in DDL, the dialect's compiler class may need to alter its
``get_column_specification()`` method to support this as well.
The ``UserDefinedType.get_col_spec()`` method will also receive
``type_expression`` if it provides ``**kw`` in its argument
signature.
fixes #3074

for memoization on a class that uses slots.
- apply many more __slots__.  mem use for nova now at 46% savings