Rails 4.2 Support

WIP branch. Author of previous PR removed source repository and I decided to create my own.

I was able to fix issue with reverse_foreign_keys method in schema_plus/active_record/connection_adapters/mysql_adapter.rb, but tests are still broken.

Now I'm trying to find out why this statement:

      define_schema(:auto_create => true) do
        create_table :users, :force => true do |t|
          t.string :login
        end
        create_table :comments, :force => true do |t|
          t.integer :user_id
          t.foreign_key :user_id, :users, :id
        end
      end

creates FK on previous Rails versions, but not on 4.2rc2.

Any help are very appreciated.