Bug 4054 - Double-clicking the 'place hold' button can result in duplicate holds

Bug 4054 - Double-clicking the 'place hold' button can result in duplicate holds

This commit adds a new jquery function to staff-global.js, preventDoubleFormSubmit().
When used thusly: $('#form-id').preventDoubleFormSubmit();
It will prevent a submitted form from being submitted a second time.
It is currently only added to the Place Hold form in reserve/request.pl

http://bugs.koha-community.org/show_bug.cgi?id=4045
Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Tested:
Double clicking no longer causes identical double holds to be placed.
passes prove t xt t/db_dependent in line with current master.

Reminder: this will need to be added to the OPAC as well.