Updated backbone in bower.json
Change lookupIterator to work exactly like underscore.
Remove dependency on Collection.sortedIndex

It seems that Backbone.Collection.sortedIndex was removed in Backbone
v1.1.0. It's easy enough to replace with the underscore method since we
had to do that for reverseSortedIndex anyway.
Merge pull request #1 from jmorrell/backbone-v1.1.0-fix

Backbone v1.1.0 fix