- renamed PASSIVE_NORESULT to PASSIVE_NO_RESULT

- renamed PASSIVE_NORESULT to PASSIVE_NO_RESULT
- renamed PASSIVE_NO_CALLABLES to PASSIVE_NO_FETCH
- passive now propagates all the way through lazy callables,
all the way into query._get(), so that many-to-one lazy load
can load the instance via the local session but not trigger
any SQL if not available, fixes [ticket:1298] without
messing up consistency of tests added in r6201
- many-to-one also handles returning PASSIVE_NO_RESULT
for the "old" value thus eliminating the need for the
previous value even if the new value is None
- query._get() uses identity_map.get(), which has been
changed to no longer raise KeyError, thus providing
mythical time savings that didn't seem to make any
difference in how fast the unit tests ran.