Use a filter instead of recently added $format argument in get_search_form(). props WraithKenny. fixes #23850. see #15081.

git-svn-id: http://core.svn.wordpress.org/trunk@23798 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Thirteen: remove HTML5 argument for search form, using a filter instead. See #23850, closes #23701.

git-svn-id: http://core.svn.wordpress.org/trunk@23799 1a063a9b-81f0-0310-95a4-ce76da25c4cd