Inline documentation for hooks in wp-includes/capabilities.php.

props ptahdunbar, kpdesign.
fixes #25531.
Built from https://develop.svn.wordpress.org/trunk@26126


git-svn-id: http://core.svn.wordpress.org/trunk@26038 1a063a9b-81f0-0310-95a4-ce76da25c4cd