Bug 13482: Prevent race condition on printing a ReserveSlip

Bug 13482: Prevent race condition on printing a ReserveSlip

The problem has been well described by Kyle and Nicole on bug 7255
description and comment 1.

With this counter patch, I suggest to popup AFTER the return has been
confirmed. This will remove the race condition and avoid to pass
itemnumber to the pl file as in the patch submitted by Olli.

Only the borrowernumber and biblionumber are needed (transfer and op are
never used by circ/hold-transfer-slip.pl).

Test plan:
It is very hard to know all cases (at least 6) where the popup is
displayed. Try at least to get the hold and the transfer confirmation
messages.
You should get the popup if you click on "print slip" button.

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>