pushnew
macro
(pushnew item place)
Prepends item to the list place if item is not in in the list and updates
the setfable place to the new list.
make-html > (let a '(1 2 3))
it: a
make-html > (pushnew 4 a)
it: (4 1 2 3)
make-html > (pushnew 3 a)
it: (4 1 2 3)