resolved conflicts
Merge branch 'sti-expiry'

 merging
ActiveRecord passes to have exceptions within after_commit bubble up

Also, some minor changes to make most strings be symbols

A nil polymorphic relationship as being constantized on accident.  No
key needed when the relationship is nil
Testing belongs to associations with different names
Merge pull request #39 from ScotterC/nil-belongs-to

A nil polymorphic relationship as being constantized on accident.