Function: listinsert
Section: programming/specific
C-Name: listinsert
Prototype: WGL
Help: listinsert(L,x,n): insert x at index n in list L, shifting the
 remaining elements to the right.
Description:
 (list, gen, small):gen        listinsert($1, $2, $3)
Doc: inserts the object $x$ at
 position $n$ in $L$ (which must be of type \typ{LIST}). This has
 complexity $O(\#L - n + 1)$: all the
 remaining elements of \var{list} (from position $n+1$ onwards) are shifted
 to the right.
