has_one does not support preload_order option

[bkilshaw]

Currently has_one and has_many both validate against the same @valid_has_options allowing you to pass a preload_order option into has_one despite it not being supported.

There is a PR (#4505) that's been open for over a year with some discussion around has_one supporting preload_order but it would probably be good to clean this up in the meantime.

[greg-rychlewski]

Thanks :)