Bug 15584 - Staff client list errors are incorrectly styled

Bug 15584 - Staff client list errors are incorrectly styled

To Test-
1. In the Staff Client, go to Lists
   (/cgi-bin/koha/virtualshelves/shelves.pl) and create a new list with
   the same name as an existing one. --note that it has some red in it
   like an error
2. apply patch
3. In the Staff Client, go to Lists
   (/cgi-bin/koha/virtualshelves/shelves.pl) and create a new list with
   the same name as an existing one. --note that now it should be just
   yellow with black writing as an alert

Signed-off-by: Mirko Tietgen <mirko@abunchofthings.net>
Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>