db:create_indexes used to miss models defined in gems or in any non-standard placement due to the filename/constantize strategy used in the rake tasks. this commit adds

• the ability for mongoid to generally and globally know the classes which have mixed it in

• refinements (backward compatible) to the rake tasks to do their damn best to load and track all models before creating or removing indexes on them

not having a uniq index made for a model in a gem is way bad - regardless of the naming strategy or file layout of the gem.