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
Rename 'get_search_form' action to 'pre_get_search_form' to prevent collision with the filter of the same name. Make sure the filtered result is not null to prevent search form from disappearing if an action function is attached to the old hook. fixes #19321.

git-svn-id: http://core.svn.wordpress.org/trunk@23800 1a063a9b-81f0-0310-95a4-ce76da25c4cd