Fix for Bug 5540, editing slip news changes to librarian interface

Fix for Bug 5540, editing slip news changes to librarian interface

The script checks for a language-specific OPAC message and, if none
is found, preselects none of the "display location" options. This
results in the first item in the <select> behing highlighted by
default, "Librarian interface." If we want to select "slip," we
must add an explicit check for it.

Signed-off-by: Nicole Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>