fix test failures introduced by a22d8a2eb0e5 * scripts/ode/private/integrate_adaptive.m: fix stepping backwards, fix invocation of OutputFcn, fix text of some error messages * scripts/ode/private/integrate_const.m: remove use of option OutputSave * scripts/ode/private/integrate_n_steps.m: remove use of option OutputSave

%!function r = f (x)
%!  if (ischar (x))
%!    r = x;
%!  else
%!    error ("expecting character string");
%!  endif
%!endfunction

%!assert (eval ("f 10;"), "10");