Fix AssociationReflection#eager_loading_dataset not cascading eager loading correctly
Fix AssociationReflection#eager_loading_dataset not cascading eager loading correctly

This enables many_to_one to use the optimized placeholder eager
loader.  This exposed the bug, since the tests for cascading
associations for multiple levels all started with many_to_one
as the first level.

reubano/sequel,freshpay/sequel,beni55/sequel,davidbegin/sequel,t-morgan/sequel,freshpay/sequel,offshore-safety/sequel,pfarrell/sequel,seeARMS/sequel,offshore-safety/sequel,t-morgan/sequel,Marketcircle/sequel,offshore-safety/sequel,dennis-d/custom_sequel,dennis-d/custom_sequel,nju520/sequel,uhoh-itsmaciek/sequel,gferguson-gd/sequel,davidbegin/sequel,uhoh-itsmaciek/sequel,yazshel/sequel,yazshel/sequel,gferguson-gd/sequel,knut2/sequel,reubano/sequel,pfarrell/sequel,nicohvi/sequel,mpalmer/sequel,nju520/sequel,knut2/sequel,seeARMS/sequel,beni55/sequel,mpalmer/sequel,nicohvi/sequel