Reduced amount of checkout, simplifying things a bit.

[jarl-dk]

This is also to unify that revision is in context of the repository (not the local working repository)

[jarl-dk]

You should also be aware of seattlerb/rake-remote_task#19

[ktheory]

What's the motivation here?

I'm not sure that shallow clones are faster for most use cases. Some example here show shallow clones are ~89% the size of a full clone.

This patch would do the shallow clone every deploy; whereas fast checkout only downloads the changes since the last commit.

[jarl-dk]

I don't mind skipping the --depth= argument completely for stability/clarity reasons... It will also eliminate any concerns regarding is_commit_id?(revision) My personal experience though is that the size is ~50% size, only really large projects (linux kernel) goes down to ~15%