copy-seq the coord-seq in the meidum-recording-body
copy-seq the coord-seq in the meidum-recording-body

 * before, we would coerce the coord-seq to a vector (unless it
   already was a vector). This had the fortunate effect of copying the
   sequence, and the output-replaying code would modify the copied
   coord-seq, leaving the original coord-seq unmodified, such that
   things would work on subsequent output-replaying calls.

   This really is a horrible way to add output-recording-type
   specific behavior. Instead of having, e.g., an around method on
   subclasses of output-record, we check the arguments to
   generate-medium-recording-body and rely on the macro machinery to
   pass this new coord-seq to make-instance via ,@arg-list. Yuck.

slyrus/mcclim,slyrus/mcclim