Bug 8518 - Self checkout does not display debt amount if syspref AllowFineOverride...

Bug 8518 - Self checkout does not display debt amount if syspref AllowFineOverride is set to allow

If the patron has depts that prevent issuing and the system preference 'AllowFineOverride' is set to 'allow', the amount is not displayed in the user message.

Additionally, patch adds currency symbol to amount.

Test plan:
Do self checkout with patron who has debts that are over the limit.
Test with and without preference 'AllowFineOverride' set.

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>