auto merge of #8131 : Seldaek/rust/getopt_usage_newline, r=brson

auto merge of #8131 : Seldaek/rust/getopt_usage_newline, r=brson

It makes things ugly when the last thing you print is the usage() output, resulting in something like:

```
$ rust run foo.rs -h
Lala

Options:
    -h --help           display this help and exit
    -V --version        output version information and exit

$ prompt
```