Timestamp of overwritten datasets.

[rainwoodman]

The timestamp of the overwritten datasets shall be updated. Currently they are not and by ls -l it is difficult to tell if the dataset is updated, creating confusions.

A useful example is the touch command.

https://gist.github.com/JoshCheek/1224782

I checked on my linux it worked on a directory. We need to see if it works on lustre.

[rainwoodman]

It works on lustre.