Folders should maintain the directory structure for globs

When you specify a glob like `src/**/*.coffee` it should pick up all the coffee files and processing them while maintaining the directory structure.

```
└── src
    └── example
        └── test.coffee
```
should become

```
├── dest
│   └── example
│       └── test.js
└── src
    └── example
        └── test.coffee
```

when you run

```javascript
gulp.files('./src/**/*.coffee').pipe(coffee()).pipe(gulp.folder('./dest'));
```