Remove added dict comprehensions that make this patch set non python 2.6
compatible.

may be construed as the Python "and" keyword
- add notes to ORM tutorial for beginners that Python "and" keyword
is not to be used
fixes #3545

Postpone as much as possible the change of update parameters to
OrderedDict from list or tuple of pairs.

This way we won't have problems with query's update method.

To avoid penalties for updates that do not require ordering, we will
only use OrderedDict for updates that receive a tuple or list of pairs,
and all kinds of dictionaries (dict, sqlalchemy's OrderedDict, or
collections.OrderedDict) will be treateated as unordered updates, just
like we were doing before.

This way this new feature will not change how updates behave for any
existing code and will only affect those that use the new ordered
feature.

This patch reverts update tests to how they were before as well as adds
a couple of tests to confirm that OrderedDicts are really treated like
normal dicts.

Thanks to Mike Bayer for suggesting a simpler refactoring.

- changelog / version note finishing