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 - Part 2: OPAC

This commit adds a new jquery function to functions.js, preventDoubleFormSubmit().
When used thusly: $('#form-id').preventDoubleFormSubmit();
It will prevent a submitted form from being submitted a second time.
This commit uses said function to prevent double processing a hold
request from the opac.

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Rapid clicking on the place hold button no longer causes duplicate holds!
Passes prove t xt t/db_dependent in line with current master.

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>