Avoid double callbacks in Rails >= 4.1

[pacoguzman]

This PR provides the same solution like #78 but I've added a test.

I wasn't able to use any person model combination to reproduce the problem that's why I've added the NestedBattle model

[rails-bot]

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[arthurnn]

Thanks

[westonganger]

Do you think you could release version 1.1.4 with this fix?