Incorrect expected result in subsequent finds using read commited isolation level

[Ronaldo Maia]

When using read-commited isolation level and running the same store.find()
query after another transaction has committed, doesn't update the results.
For example:

I have 2 stores (s1 and s2). First I get the existing objects in s1:

>>> results = s1.find(ClientCategory)
>>> print [i.name for i in results]
[u'foo']

Now I modify the object in s2:

>>> c2 = s2.find(ClientCategory, ClientCategory.name == 'foo').one()
>>> c2.name = 'bar'
>>> s2.commit()

And re-run the first query:

>>> results = s1.find(ClientCategory)
>>> print [i.name for i in results]
[u'foo']

The object was not updated.

I can see that after running the Select for the second query, the values are
fetched correctly, but _set_values(..., keep_defined=True) (store.py, line
714, inside _load_object) [1] is preventing from setting the updated values,
when the object is already in the cache.

[1] http://bazaar.launchpad.net/~storm/storm/trunk/view/452/storm/store.py#L711