fix adaptive strategy in ode solvers. * script/ode/ode45.m: remove unused option OutputSave * script/ode/private/integrate_adaptive.m: rewrite algorithm to be more compatible. * script/ode/private/runge_kutta_45_dorpri.m: use kahan summation for time increment.

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

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