Add a warning when the user adds a record to a temporary list.
TPAC has been modified so that a user will see a warning before adding
a record to a temporary bookbag. This message serves to inform the
user that they are adding to a temporary list that will disappear when
their session ends.
A new org. unit setting has been added,
opac.patron.temporary_list_warn, that will enable this warning when
set. Sites may choose not to display this warning.
The user may also set a preference in their search preferences to
disable this warning. The setting only works when a user is logged
in, of course.