Test case for ipfs update.

[Stebalien]

Write a sharness test that:

1. Starting from the current release, then the previous release, then the release before that (installed with ipfs-update).
2. Initializes a repo.
3. Starts and stops the daemon. Maybe adds and cats a file?
4. Builds a fake dist for the current branch.
5. Runs ipfs update $currentbranchbuild.
6. Checks to make sure ipfs daemon works. Starts and stops the daemon, possibly catting the same file from step 3.

[Stebalien]

@chriscool does this sound like something you could put together? Basically, we don't have anything that actually tests that the ipfs update command always works.