Bug 10359: transform masthead dropdown after user JS for CCSR

Bug 10359: transform masthead dropdown after user JS for CCSR

Since libraries may want to customize the options in the masthead search
dropdown, which is done via dropdown, it would be better if the select
box were transformed *after* user javascript was run.

To test:
1) Switch to the CCSR OPAC theme.
2) Add some Javascript to your OpacUserJS that will modify the masthead
   search dropdown, such as:
   $("select[name='idx']").append("<option value='Host-item,wrdl'>Journal title</option>");
3) Note that when you view the OPAC, the results in the dropdown are unchanged.
4) Apply patch.
5) Note that your new option now shows up.
6) Sign off.

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
(cherry picked from commit ff2b4d1ff5992989478f83517d95f957c4af50d4)
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>