Bug 10473 - Max length should be 2 digit for adding multiple copies in add items...

Bug 10473 - Max length should be 2 digit for adding multiple copies in add items page

As per the discussion, a prompt on a hard coded soft-limit is
far more acceptable as a solution.

TEST PLAN
---------
 0) Back up your DB. -- because a backup is always good!
 1) Log in to staff client
 2) Navigate to any biblio details
    (e.g. cgi-bin/koha/catalogue/detail.pl?biblionumber=#####)
 3) Click the 'Edit' dropdown button.
 4) Click 'Edit items'.
 5) Click 'Add multiple items'
 6) Enter a crazy high number (e.g. 999)
 7) Click 'Add'
    -- Koha just adds it! YIKES!
 8) Apply patch
 9) Repeat steps 5-7
10) Click 'Cancel'
    -- Koha does not add the items.
11) Repeat steps 5-7
12) Click 'Ok'
    -- Koha does add the items.
13) run koha QA test tools
14) Restore your DB.

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>