installing joint state publisher so that it can be used by rosrun

as of right now, setup.py is installing joint_state_publisher into the global bin folder instead of joint_state_publisher's bin folder. This prevents rosrun from running this. With this patch, it will be installed in both places. 

See https://github.com/ros/xacro/issues/1 for the same discussion on xacro.
Merge pull request #23 from piyushk/patch-1

installing joint state publisher so that it can be used by rosrun