FIX #324 adding empty dirs to deb package

This doesn't look wrong, but doesn't look correct either :/ So we have

```
pDir = target
pIncludes = Array(dirName)
pExclues = null // nothing to exclude
pMapper = Array(permMapper)
```

This means that if you add a directory producer with an empty directory and exclude all it's contents (the way before), the empty directory doesn't get created? Sounds for me more like a bug in jdeb. @tcurdt @ebourg may know more about this?