if we are coercing straight from string.  [ticket:2899]
- rework the tests here to be individual

the indexing.  this is for more natural operation.
- also add cast() to the JSON expression to complement astext. This integrates
the CAST call which will be needed frequently.  Part of [ticket:2687].
- it's a little unclear how more advanced unicode attribute-access is going to go,
some quick attempts at testing yielded strange error messages from psycopg2.
- do other cross linking as mentioned in [ticket:2687].

will now apply the given type to the given literal value on the
bind parameter side according
to the type given to the cast.   This essentially replaces what would
normally be the detected type of the literal value.   This only
takes effect if the auto-detected type of the literal value is either
"nulltype" (e.g. couldn't detect)
or a type that is of the same "affinity" as the cast type.
The net change here is that the :func:`.cast` function includes more
of the functionality already present in the :func:`.type_coerce` function.

- add support for "standalone" JSON objects; this involves getting CAST
to upgrade the given type of a bound parameter.  should add a core-only test
for this.
- add tests for "standalone" json round trips both with and without unicode
- add mechanism by which we remove psycopg2's "json" handler in order to get
the effect of using our non-native result handlers

more flexible ways to set up bound parameters and return types;
in particular, a :func:`.text` can now be turned into a full
FROM-object, embeddable in other statements as an alias or CTE
using the new method :meth:`.TextClause.columns`.
[ticket:2877]