get_search_form can only be used once

[mtdewvirus]

get_search_form only works once on any given page view. It uses locate_template with the load option set to true. This calls load_template, which uses require_once to load the template file. Any more attempts to display the search form on a page will fail.

Many themes will display the search form in the header area. If this is the case, the function doesn't work for Search widgets or if a search form is displayed on an error page.

[ryan]

(In [11430]) Allow multiple search form templates. Props mtdewvirus. fixes #9908