named-structure-symbol missing scl: in 3600-low

[James J. Cherry <cherry@VALLECITO.SCRC.Symbolics.COM>]

The call to named-structure-symbol in iwmc-class-p (from 3600-low) is
missing the scl: pkg.

The other bug is that iwmc-class-p gets called with a symbol as its arg,
which scl:named-structure-symbol barfs about.  It needs to arrayp the
arg first:

(scl:defsubst iwmc-class-p (x)
  (and (arrayp x)
       (eq (scl:named-structure-symbol x) 'iwmc-class)))