Bug 6935: Correct XISBNDailyLimit for new installations

Bug 6935: Correct XISBNDailyLimit for new installations

This corrects the value of XISBNDailyLimit in the system preferences
installation file to 999 instead of 499.

The file was missed in an earlier update, so new installations
have different values than older installations that were updated.

Another patch with a database update is needed. Sending this patch first,
until it's clear how database updates will work for 3.8.

To test:
1) Recreate your database from scratch
2) Check your system preference XISBNDailyLimit shows 999 instead of 499,
matching the description of the system preference.

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>