OPTIONAL
SYNOPSIS
mixed * intersect_alist (mixed * list1, mixed * list2)
DESCRIPTION
Does a fast set intersection on alist key vectors (NOT on full alists!).
The operator '&' does set intersection on arrays in general.
EXAMPLE
new_list = intersect_alist(list1, list2);
SEE ALSO
filter_array(E), assoc(E), insert_alist(E), map_array(E),
member_array(E), order_alist(E), sort_array(E), unique_array(E)