cargo fmt has surprising behavior in a workspace without --all

[sgrif]

I had recently gotten out of the habit of type --all since it seemed that cargo fmt did what I wanted without it when I ran it from the root of the workspace. However, after a build failure that occurred when updating to 0.3.1 (unrelated: that was a surprising amount of churn...), I noticed that cargo fmt when run in Diesel's root directory is only formatting the diesel repo, and nothing else. I'm assuming it's choosing that because that directory is the first of our 23 workspace members.

This is really surprising behavior. I would expect it to either:

• Do exactly the same thing as cargo fmt --all
• Error and complain that I'm in a workspace, not a real project.