workaround for issue #474

this is workaround for issue #474
However I wrote this patch without knowing what is the expected behavior of using grooup/remap/param , is there any specification on this?

> The roslaunch wiki page contains all the information available.

yes, but it is not explicitly written that remap changes node name but not affect param , so if you remap node name like follows:
```
<launch>
  <remap from="/joy" to="/joy_remap"/>
  <node pkg="joy" type="joy_node" name="joy" output="screen">
    <param name="dev" type="string" value="/dev/input/js1" />
  </node>
</launch>
```
you have to change param name setting as 
```
    <param name="/joy_remap/dev" type="string" value="/dev/input/js1" />
```


I don't think this is the right place to modify the behavior. The namespace of the surrounding node `param_ns.ns` should already contain the remapped name instead.