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.
Built from https://develop.svn.wordpress.org/trunk@28645


git-svn-id: http://core.svn.wordpress.org/trunk@28463 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugin activation/deletion errors should be styled as such.

props johnbillion.
fixes #28260.
Built from https://develop.svn.wordpress.org/trunk@28646


git-svn-id: http://core.svn.wordpress.org/trunk@28464 1a063a9b-81f0-0310-95a4-ce76da25c4cd