Rename several images

Gives every finished image in ids the same name followed by its place in upload order, oldest first: trip-01, trip-02. The number has at least two digits, more when the count needs them. A single image gets the name alone. Images that haven't finished are passed over, and if none has, the call is refused. It is all or nothing: when one of the names would be too long, none changes. Every id has to be one of your images; the ones that aren't are named in errors.