Find all models across all namespaces
===

I want to find all models in *all* namespaces.

Ideas I've considered:

* `Object.constants` is not working a good starting point because it does not find my namespaced modules. So [this answer](http://stackoverflow.com/a/9853016/109618) isn't working for me.

* [ObjectSpace](http://www.ruby-doc.org/core-1.9.3/ObjectSpace.html) is a possibility but I'd rather not use it unless necessary, since it seems less portable across Ruby implementations. (See also: [ObjectSpace is disabled by default in JRuby](http://kenai.com/projects/jruby/pages/PerformanceTuning#Disabling_ObjectSpace).)


