That is, after exhausing all rows using the fetch methods, the
DBAPI cursor is released as before and the object may be safely
discarded, but the fetch methods may continue to be called for which
they will return an end-of-result object (None for fetchone, empty list
for fetchmany and fetchall).   Only if :meth:`.ResultProxy.close`
is called explicitly will these methods raise the "result is closed"
error.
fixes #3330 fixes #3329

unfortunately Sphinx refuses to work correctly for the columns
attribute so we just add a lame message to contains_column().

conventions that include the token ``%(column_0_name)s``; the
constraint expression is scanned for columns.  Additionally,
naming conventions for check constraints that don't include the
``%(constraint_name)s`` token will now work for :class:`.SchemaType`-
generated constraints, such as those of :class:`.Boolean` and
:class:`.Enum`; this stopped working in 0.9.7 due to :ticket:`3067`.
fixes #3299

Connection.connection and engine.raw_connection()

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