folded_equivalents busted, no unit tests

[Mike Bayer]

people.join(managers).outerjoin(boss) in polymorph.py does not fold properly if you apply select(folded_equivalents=True) to it

[Mike Bayer]

OK we don't actually need folded_equivalents in any current case, I had forgotten that it's name oriented so its not terribly relevant and I'd almost like to remove it altogether, but it is useful for some hypothetical "union"s since our union() construct uses column names to match cols together (also something im not sure I like).

[Mike Bayer]

#1131 calls for removal of the feature altogether

[Mike Bayer]

Removing milestone: 0.4.xx (automated comment)