adjust ActiveRecord::Base.all_models for rails3

the old method included Profile but excluded CourseProfile. but in
rails3, Profile.table_name is nil because it's an abstract class;
including it meant trying to truncate table "" in spec_helper.rb, but
excluding it without including CourseProfile meant the "profiles" table
didn't get truncated.

update the model listing to exclude abstract classes (e.g. Profile), but
include direct descendants of abstract classes (e.g. CourseProfile), but
not direct descendants of non-abstract classes (e.g. Announcement).

Change-Id: I4e6a60b302f1c88f4ace0c7d41377e92eeecfaa1
Reviewed-on: https://gerrit.instructure.com/27087
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: Jacob Fugal <jacob@instructure.com>
Product-Review: Jacob Fugal <jacob@instructure.com>

config/initializers/active_record.rb

@@ -26,7 +26,9 @@ class ActiveRecord::Base
     @all_models = (ActiveRecord::Base.send(:subclasses) +
                    ActiveRecord::Base.models_from_files +
                    [Version]).compact.uniq.reject { |model|
-      model.superclass != ActiveRecord::Base || (model.respond_to?(:tableless?) && model.tableless?)
+      !(model.superclass == ActiveRecord::Base || model.superclass.abstract_class?) ||
+      (model.respond_to?(:tableless?) && model.tableless?) ||
+      model.abstract_class?
     }
   end