Sadly, rust no longer has {:u} and {:s} formatters

`{:u}` and other formatters have an important function of parameter
typechecking. E. g. code like this:

``` println!("Found {:u} files", count); ```

didn't compile after I change `count` from `uint` to `Option<uint>`
during refactoring. That's what I expect from statically typed
language.

And now I have to write:

``` println!("Found {} files", count); ```

and program happily prints something like `Found Some(36) files`.
fix repeated packed enum

fixes #45