Allowed Chrome to optimize Collection.set and RelationalModel.extend.
Perhaps will help #480?
Merge branch 'coll-set-optimizations' of https://github.com/AsymmetricVentures/Backbone-relational into AsymmetricVentures-coll-set-optimizations
Pick a few optimizations, convert `getReverseRelations` to for loops (seems to be a hotspot).
Merge branch 'AsymmetricVentures-coll-set-optimizations'