fix asset_packager loading for rails threadsafe mode
fix asset_packager loading for rails threadsafe mode

When dependency_loading == false, which is true when
running rails in threadsafe mode we can't count on classes
being automagically loaded.

See: 
http://github.com/sandofsky/asset_packager/commit/c925976caac2138f94c979e64277b2da5f537239
concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse