Pagination fix

[davidw]

This is based on the work here:

https://github.com/amatsuda/kaminari/pull/573

But includes a fix for this change:

rails/rails#18379

[yuki24]

Many specs including the newly added specs are failing. This code would also introduce a dependency that is a private Rails API and I'm not sure if we should go with this.

[davidw]

I'll look into the specs.

I don't see any perfect solutions to the problem this addresses:

• Ignore it. This lets bugs slip into people's code, which is why it came to my attention in the first place - one of our API's was returning way fewer pages than it should have because a GROUP BY got added at a certain point.
• Decide that it just can't do that, and throw an exception if you try and use something with a GROUP BY. That'd at least make things very clear.
• Something like this solution.
• Other ideas?

Thank you!

[davidw]

Locally, the activerecord 4* tests pass, but 32 does not work at all:

home/davidw/.rvm/gems/ruby-2.2.2/gems/activesupport-3.2.22.5/lib/active_support/dependencies.rb:251:in require': cannot load such file -- test/unit/assertions (LoadError)`

[yuki24]

I'm closing this issue in favor of #573.

[yuki24]

But thank you for your contribution!