check if compostite_class is of class type

before checking if it is a subclass of `MutableComposite`
make tests pass
The resolution of :class:`.ForeignKey` objects to their
target :class:`.Column` has been reworked to be as
immediate as possible, based on the moment that the
target :class:`.Column` is associated with the same
:class:`.MetaData` as this :class:`.ForeignKey`, rather
than waiting for the first time a join is constructed,
or similar. This along with other improvements allows
earlier detection of some foreign key configuration
issues.  Also included here is a rework of the
type-propagation system, so that
it should be reliable now to set the type as ``None``
on any :class:`.Column` that refers to another via
:class:`.ForeignKey` - the type will be copied from the
target column as soon as that other column is associated,
and now works for composite foreign keys as well.
[ticket:1765]
tweak this for now, would need a test
sort here so that exception messages are testable
Merge branch 'master' of https://github.com/asldevi/sqlalchemy into some_branch
- add a test for pullreq 8
- simplify
0.9 changelog
0.8 changelog
doc fixes
docs
YEAR(2) emits a warning and oursql / mysqlconnector throw an exception
on the warning so just dump it