additional list seeking transformations

additional list seeking transformations

 * Implement TRANSFORM-LIST-PRED-SEEK, very much akin to
   TRANSFORM-LIST-ITEM-SEEK, and use it to optimize MEMBER-IF[-NOT],
   ASSOC-IF[-NOT], and RASSOC-IF[-NOT].

 * Implement full versions of list seeking functions in terms of the
   specialized versions: in some cases this is a win, in some cases a
   loss -- but the number of places where functionality is duplicated
   is reduced, which should be easier on the maintenance and less
   bug-prone.

 * Add a TRANSFORM-LIST-ITEM-SEEK transform for RASSOC.

 * LVAR-FOR-NAMED-FUNCTION was a restricted form of LVAR-FUN-IS.  Do
   away with the former, and move the latter to ir1util.lisp.