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Remove duplication for include/exclude options in backwards_compatibilize.
Simplify check for String include/exclude option.
Merge pull request #1284 from mojombo/include-exclude-deprecation-simplification

Include exclude deprecation simplification
Update history to reflect merge of #1284.
Merge pull request #1271 from sanandnarayan/related_posts

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Update history to reflect merge of #1271.