simplify RDFLoader & provide more/better error message (#173)
simplify RDFLoader & provide more/better error message (#173)

This came up because the code didn't complain when robot_description wasn't set.

ros-planning/moveit,ros-planning/moveit,v4hn/moveit,ros-planning/moveit,davetcoleman/moveit,davetcoleman/moveit,ros-planning/moveit,ros-planning/moveit,davetcoleman/moveit,v4hn/moveit,v4hn/moveit,davetcoleman/moveit,v4hn/moveit