teach copy alerts how to automatically generate certain overrides

teach copy alerts how to automatically generate certain overrides

When a new-style copy alert type is active but supressed, any
system-generated events of that type should be recorded but
not present a pop-up. In some cases, an older-style circ event
make get generated; this patch supplies a way for the new copy
alerts to override the old-style events without having
to sprinkle a bunch of special checks.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>