ADJOIN
======

syntax: (adjoin <element> <list> [:test <test>])

This function searches in the list for the element.
If the element is included in the list, then adjoin
will return the list, otherwise a list with the
<element> as the first element and the <list> as
rest will be returned.

example:       >(adjoin 2 '(1 2 3))
               (1 2 3)
               >(adjoin 0 '(1 2 3))
               (0 1 2 3)