rails4: fix activerecord all_models

fixes a circular dependency error trying to load
 AccountAuthorizationConfig::CAS

refs #CNVS-21596

Change-Id: I65f92e2cc09228f19363b1964e063a2a5fcde037
Reviewed-on: https://gerrit.instructure.com/57645
Tested-by: Jenkins
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>

config/initializers/active_record.rb

@@ -53,8 +53,7 @@ def feed_code
 
   def self.all_models
     return @all_models if @all_models.present?
-    @all_models = (ActiveRecord::Base.send(:subclasses) +
-                   ActiveRecord::Base.models_from_files +
+    @all_models = (ActiveRecord::Base.models_from_files +
                    [Version]).compact.uniq.reject { |model|
       !(model.superclass == ActiveRecord::Base || model.superclass.abstract_class?) ||
       (model.respond_to?(:tableless?) && model.tableless?) ||
@@ -63,19 +62,14 @@ def self.all_models
   end
 
   def self.models_from_files
-    @from_files ||= Dir[
-      "#{Rails.root}/app/models/**/*.rb",
-      "#{Rails.root}/vendor/plugins/*/app/models/**/*.rb",
-      "#{Rails.root}/gems/plugins/*/app/models/**/*.rb",
-    ].sort.collect { |file|
-      model = begin
-          file.sub(%r{.*/app/models/(.*)\.rb$}, '\1').camelize.constantize
-        rescue NameError, LoadError
-          next
-        end
-      next unless model < ActiveRecord::Base
-      model
-    }
+    @from_files ||= begin
+      Dir[
+        "#{Rails.root}/app/models/**/*.rb",
+        "#{Rails.root}/vendor/plugins/*/app/models/**/*.rb",
+        "#{Rails.root}/gems/plugins/*/app/models/**/*.rb",
+      ].sort.each { |file| ActiveSupport::Dependencies.require_or_load(file) }
+      ActiveRecord::Base.descendants
+    end
   end
 
   def self.maximum_text_length