when loading mapped entities.   The function overhead of applying
a per-object deferred callable to an instance at load time was
significantly higher than that of just loading the data from the row
(note that ``defer()`` is meant to reduce DB/network overhead, not
necessarily function call count); the function call overhead is now
less than that of loading data from the column in all cases.  There
is also a reduction in the number of "lazy callable" objects created
per load from N (total deferred values in the result) to 1 (total
number of deferred cols).
[ticket:2778]

actual mock objects from the mock library.  I'd like to use mock
for new tests so we might as well use it in obvious places.
- use unittest.mock in py3.3
- changelog
- add a note to README.unittests
- add tests_require in setup.py
- have tests import from sqlalchemy.testing.mock
- apply usage of mock to one of the event tests.  we can be using
this approach all over the place.

labeled columns when apply_labels() is used; this mode
produces a SELECT where each column is labeled as in
<tablename>_<columnname>, to remove column name collisions
for a multiple table select.   The fix is that if two labels
collide when combined with the table name, i.e.
"foo.bar_id" and "foo_bar.id", anonymous aliasing will be
applied to one of the dupes.  This allows the ORM to handle
both columns independently; previously, 0.7
would in some cases silently emit a second SELECT for the
column that was "duped", and in 0.8 an ambiguous column error
would be emitted.   The "keys" applied to the .c. collection
of the select() will also be deduped, so that the "column
being replaced" warning will no longer emit for any select()
that specifies use_labels, though the dupe key will be given
an anonymous label which isn't generally user-friendly.
[ticket:2702]

- other cleanup
- don't need compat.decimal, that approach never panned out. hopefully
outside libs aren't pulling it in, they shouldn't be

- Fixed potential memory leak which could occur if an
arbitrary number of :class:`.sessionmaker` objects
were created.   The anonymous subclass created by
the sessionmaker, when dereferenced, would not be garbage
collected due to remaining class-level references from the
event package.  This issue also applies to any custom system
that made use of ad-hoc subclasses in conjunction with
an event dispatcher.  Also in 0.7.10. [ticket:2650]

- paths now store Mapper + MapperProperty now instead of string key,
so that the parent mapper for the property is known, supports same-named
properties on multiple subclasses
- the Mapper within the path is now always relevant to the property
to the right of it.  PathRegistry does the translation now, instead
of having all the outside users of PathRegistry worry about it,
to produce a path that is much more consistent.  Paths are now
consistent with mappings in all cases.  Special logic to get at
"with_polymorphic" structures and such added also.
- AliasedClass now has two modes, "use_mapper_path" and regular;
"use_mapper_path" is for all those situations where we put an AliasedClass
in for a plain class internally, and want it to "path" with the
plain mapper.
- The AliasedInsp is now the first class "entity" for an AliasedClass,
and is passed around internally and used as attr._parententity
and such.  it is the AliasedClass analogue for Mapper.

at this point