specify a :func:`.text` expression as the target; the index no longer
needs to have a table-bound column present if the index is to be
manually added to the table, either via inline declaration or via
:meth:`.Table.append_constraint`. fixes #3028

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

applied to :class:`.Constraint` and :class:`.Index` objects.  Based
on a recipe in the wiki, the new feature uses schema-events to set up
names as various schema objects are associated with each other.  The
events then expose a configuration system through a new argument
:paramref:`.MetaData.naming_convention`.  This system allows production
of both simple and custom naming schemes for constraints and indexes
on a per-:class:`.MetaData` basis.  [ticket:2923]

commit 7e65e52c086652de3dd3303c723f98f09af54db8
Author: Mike Bayer <mike_mp@zzzcomputing.com>
Date:   Sat Feb 1 15:09:04 2014 -0500

    - first pass at new naming approach