Two fixes for package xml exports
Two fixes for package xml exports

Without the .items() you have the error:

```
[error] too many values to unpack : <type 'exceptions.ValueError'>
```

The space also makes sure the tag and attributes are separated.

aleksandaratanasov/catkin_pkg,harmishhk/catkin_pkg,ipa-mdl/catkin_pkg,davetcoleman/catkin_pkg