Build error: JointConstSharedPtr used from urdf and no more boost

[geiser1u]

I raise this issue mainly to help people who like me would like to use this plugin with the latest version of ros_control. I struggled to find the source of the build error I got so I think it might be helpful for others.
Since the ros_control issue referenced at this address: https://github.com/ros-controls/ros_control/pull/251/files, an urdf JointConstSharedPtr is used compared to the boost one which was previously used. This leads to build error because steer_bot_hardware_gazebo assumes that the boost version is used. To fix this issue, the line 63 in the source code must be replaced by the following:
urdf::JointConstSharedPtr urdf_joint = urdf_model->getJoint(name);