Bug 9761: dbrev for ConfirmFutureHolds

Bug 9761: dbrev for ConfirmFutureHolds

Db rev for new pref ConfirmFutureHolds.

Test plan:
Run [your server]/cgi-bin/koha/installer/install.pl?step=3&op=updatestructure
Optionally, run a new install to test sysprefs.sql.
Or:
Edit sysprefs.sql, leave at least the last few lines including the new one.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>