in 0.7.4, which ensures that the connection
is in a valid state before attempting to call
rollback()/prepare()/release() on savepoint
and two-phase transactions.

    ForeignKeyConstraint refers to a column name in
    the parent that is not found.
- add tests for [ticket:2226], as if we hit each @declared_attr
directly with obj.__get__(obj, name) instead of using
getattr(cls, name).  Basic inheritance mechanics are improperly
used in this case, so 2226 is invalid.

to column server_onupdate, it would not
have its parent "column" assigned, added
test coverage for all column default assignment
patterns.  [ticket:2147]

connections that were discarded via overflow or periodic
cleanup() were not explicitly closed, leaving garbage
collection to the task instead.   This generally only
affects non-reference-counting backends like Jython
and Pypy.  Thanks to Jaimy Azle for spotting
this.  [ticket:2102]

    'doc' attribute.  [ticket:2028]

begin_nested(); engine then implements contextmanager
methods to allow the "with" statement. [ticket:2004]

and '_create_rule' attributes within a copy()/tometadata()
[ticket:2000]