Allow "ns:name" attributes in xml node attributes, if namespace specified

allow xml node definitions to use xml namespaces, and parse attributes using the namespace prefix:

```{.xml}
<project xmlns:myns="http://blah">
<node name="mynode" myns:something="asdf" myns:something-else="wombat"/>
</project>
```

result:

![screen shot 2014-05-12 at 3 47 44 pm](https://cloud.githubusercontent.com/assets/55603/2951430/90a60b2c-da27-11e3-9494-a265a7822af9.png)