mark a constraint name as already having had a naming convention applied.
This token will be used by Alembic migrations as of Alembic 0.6.4
in order to render constraints in migration scripts with names marked
as already having been subject to a naming convention.
re: #2991

apply to :class:`.CheckConstraint` objects that are associated
directly with a :class:`.Column` instead of just on the
:class:`.Table`.

where the name of a check constraint making use of the
`"%(constraint_name)s"` token would get doubled up for the
constraint generated by a boolean or enum type, and overall
duplicate events would cause the `"%(constraint_name)s"` token
to keep compounding itself.
fixes #2991

or :meth:`.MapperEvents.after_configured` events are applied to a
specific mapper or mapped class, as the events are only invoked
for the :class:`.Mapper` target at the general level.

and :func:`.event.listens_for`.  This is a convenience feature which
will wrap the given listener such that it is only invoked once.

The selectable is the third argument to with_polymorphic.

- various improvemnts to oracle docs, rewrite section on unicode, more linking,
enhance section on resolve_synonyms

connection to be returned might get inadvertently cleaned out during
the "cleanup" process.  Patch courtesy jd23.

(e.g. ``x[:] = [...]``) would fail on Py3k.