Request: Fix naming of .ckpt when resuming training

[cfragkos]

Right now when you train (lets say to 1200 steps saving every 400) you get name-400, name-800, name-1200, name The last two basically being the same. If you resume for another 400 steps you will get name-400 (instead of name-1600) overwriting the last steps-400 too which makes it a mess keeping tabs on your checkpoints. Could you fix it up?