Run "go fmt" on all .go files

Since [gofmt'd code is](http://blog.golang.org/go-fmt-your-code):

> - easier to write: never worry about minor formatting concerns while hacking away,
> - easier to read: when all code looks the same you need not mentally convert others' formatting style into something you can understand.
> - easier to maintain: mechanical changes to the source don't cause unrelated changes to the file's formatting; diffs show only the real changes.
> - uncontroversial: never have a debate about spacing or brace position ever again!