Reimplement leach so that stack is clean when executing the quotation

The previous implementation let garbage on the stack (such as the lazy list
cdr) before executing the quotation. This prevents easy implementation of
reduce-like words using leach.

extra/lazy-lists/lazy-lists.factor

@@ -100,11 +100,7 @@ M: lazy-cons list? ( object -- bool )
     dup car swap cdr ;
 
 : leach ( list quot -- )
-  swap dup nil? [
+  swap dup nil? [ 2drop ] [ uncons swapd over 2slip leach ] if ; inline
-    2drop
-  ] [
-    uncons swap pick call swap leach
-  ] if ;
 
 TUPLE: memoized-cons original car cdr nil? ;