Removes unnecessary require() in Associations/Many.js
Changes Singleton to avoid cache if save_check option is enabled and cached instance is not saved (#78)
Adds default setting instance.cacheSaveCheck = true (#78)
Changes Model to pass instance.cacheSaveCheck setting to Singleton (#78)
Fixes test-get-cache test for new behaviour (#78)
Adds test for cached Model.get() with instance.cacheSaveCheck disabled (#78)