Replace be_true/false matcher with == true/false, as RSpec 3.0 drops the former
Let Travis CI also test on Ruby 2.1; skip incompatible Ruby-Rails combinations
Add Rails 4.1 support
Update gem version in test apps
Satisfy Travis CI: Do not install SlimGems, downgrade Rubygems on Ruby 1.8 instead
Improve Util.define_scope: support all valid find options