1.0.23.25: better errors for bogus RECURSIVE-P in reader

1.0.23.25: better errors for bogus RECURSIVE-P in reader

 * When RECURSIVE-P was true in a non-recursive context, we used to
   signal an unbound-variable error. Now signal a sensible
   reader-error instead.

 * Patch by Tobias Rittweiler. Also apologies for constant mistyping
   of his name: mentally s/Ritter/Ritt/ in historical commit
   messages...