Backport "Fix in [] to be false, in [] to be true"

This is in response to discussion at rails/rails#9216
The original commit was in response to discussion on 62207fa
Merge pull request #174 from eduardordm/master

Revert fixes involving issue #99 (which makes Arel unusable in large datasets)
Conflicts:
	lib/arel/visitors/oracle.rb
	test/visitors/test_oracle.rb
update Gemfile
Merge pull request #186 from CrowdFlower/update_gemfile

Update Gemfile