Fix intersection equality error

[jcoveney]

closes #877

[jcoveney]

Would love to get a test in for this if I have time tomorrow but otherwise this fixes it

[ianoc]

PR/changes look fine, though I'm slow to close this with out any other issues/tests since obviously this was quite broken before... (looks like there have been many issues with this skew join going back)

[jcoveney]

I'll try and add a test, should be easy to do

[jcoveney]

This is actually something tricky to test for...since if it thinks there is a collision it then renames and then names back, I don't think there was actually a bug. It was just going through an extra renaming step.

[johnynek]

I agree that this is not a bug, but a performance optimization that was not being triggered due this bug (lack of type safety on ==).

I also agree that the .isEmpty fix here is the right way.

[jcoveney]

Click that M button :)