- Updated documentation for JSON class

 - Added support for additional operators
 - Made return as json default (rather than text)

 - Removed unneeded import of psycopg2.extensions

 - Fixed reference to HSTORE
 - Corrected spelling of SQLAlchemy

 sqlalchemy/dialects/postgresql/psycopg2:
 - Added psycopg2 specific wrapper type for JSON which uses inherent json deserialization facilities
 - Added code to detect and utilize the JSON wrapper if psycopg2 >= 2.5

test/dialect/postgresql/test_types:
- removed reference to use_native_hstore

- Added import references to JSON class

 sqlalchemy/dialects/postgresql/base.py:
 - Added visitor method for JSON class

 sqlalchemy/dialects/postgresql/pgjson (new):
 - JSON class, supports automatic serialization and deserialization of json data, as well as basic json operators.

have been modified, such that the COLLATE operator is now of lower
precedence than the comparison operators.  This has the effect that
a COLLATE applied to a comparison will not render parenthesis
around the comparison, which is not parsed by backends such as
MSSQL.  The change is backwards incompatible for those setups that
were working around the issue by applying :meth:`.Operators.collate`
to an individual element of the comparison expression,
rather than the comparison expression as a whole. [ticket:2879]

automatic reflection support for the "secondary" table referred
to by a :func:`.relationship`.   "secondary", when specified
either as a string table name, or as a :class:`.Table` object with
only a name and :class:`.MetaData` object will also be included
in the reflection process when :meth:`.DeferredReflection.prepare`
is called. [ticket:2865]
- clsregistry._resolver() now uses a stateful _class_resolver()
class in order to handle the work of mapping strings to
objects.   This is to provide for simpler extensibility, namely
a ._resolvers collection of ad-hoc name resolution functions;
the DeferredReflection class adds its own resolver here in order
to handle relationship(secondary) names which generate new
Table objects.