Twenty Fourteen: change hardcoded pagination base to use the WordPress Rewrite object's `pagination_base` value instead. Document global variable usage properly.

Props SergeyBiryukov, fixes #28405.
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git-svn-id: http://core.svn.wordpress.org/trunk@28463 1a063a9b-81f0-0310-95a4-ce76da25c4cd