Hardlinks won't really work as a snapshot substitute; any files that are modified (rather than deleted/rewritten) will be modified in the "snapshot" as well. A hardlink "snapshot" like that would protect against accidental deletion, but that's about it.
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No. The reason it does not exist is because the Ares-I kept running into delays and cost overruns, as well as performance issues that continually forced them to remove capabilites for Orion. The reason it _shouldn't_ exist is that it's a _terrible_ program that, had it been allowed to continue, would quite probably have killed NASA and never gotten us out of LEO anyway. Even the Ares-I would not have been operational during Obama's presidency, even presuming he stays in office until 2016.
I used to be a fan of Constellation when all I knew was the current NASA PR. After learning just what an absolute mess the program really was, and the severe issues with the Ares-I, I've changed my mind. While the Ares-I would probably be possible to finish, the expected cost of development is $35 billion dollars, and not before 2017. And at the end of all that time and money, you end up with a rocket that takes less mass to LEO than the Falcon 9 Heavy will - and the F9H will have cost roughly as much to fully develop from scratch as the Ares-I's expected yearly recurring operating cost.
It is also worth pointing out that the budget that cancels Constellation is NOT in effect yet, and won't be until next year; congress still has to approve it. Obama has absolutely nothing to do with the current delays and failings of the Constellation program - the program itself, and the previous NASA administrator, bear all the blame for that.