this must have been an oversight.   Leave mysql.JSON in place still
as we might need to add things to it.
- CAST(json, String) still confusing MySQL drivers even mysqlclient.
Since here we're checking for the raw form of the JSON and not a typical
round trip, add a force for unicode

Change-Id: I727f4526a01a0875037cf0dede45cd074da5205a

Change-Id: I2dc6961f9b692a8bb6bfb2296d159df145dec679

Regarding 0e88bcc30ed49193b91f248123f526fa30007f22, "options"
needs to be present as a key in the dictionary because Alembic
uses this as a guide to know if the backend is even capable of
reporting on foreign key options.

Change-Id: I271090f75088cfeec24315a878060f9b8a265335

temp tables are reflectable on the same session they were
created

attempt integer indexed access from a key/value object nor
string access from an integer-indexed array, as earlier Postgresql
versions (prior to 9.4) don't allow this

persistence of JSON values in MySQL as well as basic operator support
of "getitem" and "getpath", making use of the ``JSON_EXTRACT``
function in order to refer to individual paths in a JSON structure.
fixes #3547
- Added a new type to core :class:`.types.JSON`.  This is the
base of the PostgreSQL :class:`.postgresql.JSON` type as well as that
of the new :class:`.mysql.JSON` type, so that a PG/MySQL-agnostic
JSON column may be used.  The type features basic index and path
searching support.
fixes #3619
- reorganization of migration docs etc. to try to refer both to
the fixes to JSON that helps Postgresql while at the same time
indicating these are new features of the new base JSON type.
- a rework of the Array/Indexable system some more, moving things
that are specific to Array out of Indexable.
- new operators for JSON indexing added to core so that these can
be compiled by the PG and MySQL dialects individually
- rename sqltypes.Array to sqltypes.ARRAY - as there is no generic
Array implementation, this is an uppercase type for now, consistent
with the new sqltypes.JSON type that is also not a generic implementation.
There may need to be some convention change to handle the case of
datatypes that aren't generic, rely upon DB-native implementations,
but aren't necessarily all named the same thing.