Add link_to_previous_page helper for sinatra
Merge pull request #504 from ikeay/fix_sinatra_previous_link

Add link_to_previous_page helper for sinatra
Add tests for mongoid 4 beta 1
Merge pull request #505 from arthurnn/mongoid4

Add tests for mongoid 4 beta 1
Do not test mongoid 4.0 with Ruby 1.8.7
Mongoid 4.0 with rubinius is still unstable so just allow it to fail

Also, AR edge with jruby has been stable for a while, so do not allow it
to fail.