add 2-arg form to query.join(), supercedes tuple form (but don't deprecate)

[Mike Bayer]

this involves working out the logic to detect the "old" calling style and test heavily.

the "three arg" form, (left, right, onclause), can be released after 0.7.0.

[Mike Bayer]

this is a very easy change and most of the work involves changing the tests, patch is attached.

[Mike Bayer]

change the deprecation warning to pending deprecation. the current calling style shouldn't produce warnings for 0.7.

[Mike Bayer]

the ORM tutorial is not up to date yet, still says "we use a tuple", probably shouldn't talk about the tuple form for now

[Mike Bayer]

ee25562461db46e31643a2f4ff9c981313a52dc3

[Mike Bayer]

Removing milestone: 0.7.0 (automated comment)