code cleanup of data_cube, made default function more interesting
code cleanup of data_cube, made default function more interesting

tommy-u/chaco,tommy-u/chaco,ContinuumIO/chaco,ContinuumIO/chaco,burnpanck/chaco,ContinuumIO/chaco,burnpanck/chaco,ContinuumIO/chaco,burnpanck/chaco,tommy-u/chaco