support cpanfile extra args

```
requires 'Plack';
requires 'Plack', '0.9970';
requires 'Plack', git => 'git://github.com/plack/Plack.git', revision => '0.9970';
requires 'Plack', '0.9970', git => 'git://github.com/plack/Plack.git', revision => '0.9970';

# and

requires 'git://github.com/plack/Plack.git';
requires 'git://github.com/plack/Plack.git@0.9970';
```

are okay.