Do not merge "WHERE" conditions into last one during pagination
Due to rails merging "where" conditions with same
left hand side, queries like:

Product.where(:number => [1,2,3]).
  where(:number => [2,3,4]).page(1)

Resulted in SQL like

SELECT * FROM products WHERE number IN (2,3,4) LIMIT 25 OFFSET 0

Which was wrong. It was caused by nested attributes.
I got rid of them and used standard class method,
preferred for Rails 3.x.
1.8.x compatibility
Spec for multiple conditions for one attribute and #page args
Raise error if too many attributes given to #page
Merge branch 'master' of https://github.com/detomastah/kaminari