PHPDoc and i18n fixes for dashboard widgets.

props dimadin for initial patch.
see #25824.
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git-svn-id: http://core.svn.wordpress.org/trunk@26148 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Fix date comparison in dashboard_relative_date(). fixes #26033.
Built from https://develop.svn.wordpress.org/trunk@26242


git-svn-id: http://core.svn.wordpress.org/trunk@26149 1a063a9b-81f0-0310-95a4-ce76da25c4cd