Patch for 2-3-stable. Fix infinite loop when using has_many :through with nonstandard keys

[Aubrey Holland]

If you attempt the create a has_many :through association that uses a
has_many association with nonstandard primary and foreign keys, you
will get an infinite loop when trying to use the association. I have
written a longer description of this problem, along with a simple,
tested patch that fixes it in the following bug:

https://rails.lighthouseapp.com/projects/8994-ruby-on-rails/tickets/3628-infinite-loop-when-using-has_many-through-with-nonstandard-keys

Aubrey