*RSET -> bug introduction

[JONL at MIT-MC (Jon L White)]

    Date: 15 March 1981 22:34-EST
    From: Robert W. Kerns <RWK at MIT-MC>
    JONL, your recent change to ERRCK broke almost the entire
    extended LISP system, including VECTOR, DEFVST, and FORMAT.
    I have de-installed your change.
Actually, the change to ERRCK was right;  several other files
had bugs in them, but VECTOR, DEFVST, and FORMAT weren't among
them(!!).   SUBSEQ was one that had a bug whose manifestation
was formerly inconsequential, until I fixed the defaulting problem 
with ERRCK, as per report by BIL:
    Date: 15 March 1981 01:15-EST
    From: William G. Dubuque <WGD at MIT-MC>
	    SI:REPLACER is broken in te current version of SUBSEQ.
    (TO-VECTOR '(1 2)) => #(), likewise for TO-LIST, etc. .  .
I've fixed SUBSEQ, and several other files which used the
function SI:CHECK-SUBSEQUENCER in ERRCK.  The difficulty arose
because CHECK-SUBSEQUENCER etc weren't documented, and there were
inconsistent usages of it among the several files.  I've put documentation 
for it into NIL;NEWFUN >  under section 2.6.