How do I force loading of a non-default library?

I deployed a Ferret-enabled app to TextDrive with ferret.rb and
associated libraries installed in RAILS_ROOT/lib. For a while, I’ve
convinced Rails to load ferret.rb from there, but only by hard-coding
it. Today, with no other changes (that I’m aware of), it suddenly
stopped working and now insists on loading ferret.rb from

Is there a safe way to override the load path?

(And why doesn’t Rails try to load local libraries first, before
searching through server-wide paths?)