proposal for object-oriented dispatch on sign



I committed my patch that uses object-oriented dispatch for the 
function sign (not $sign); example

(%i2) sign(signum(x));
(%o2) pnz

(%i3) :lisp(setf (get '%signum 'sign-function) #'(lambda (s) (declare 
(ignore s)) (setq sign '$pz)))
#<Anonymous Function #xC622EE6>

(%i3) sign(signum(x));
(%o3) pz


--Barton